  
  [1X2 [33X[0;0YTutorial for the [5XGAP[105X[101X[1X Character Table Library[133X[101X
  
  [33X[0;0YThis  chapter  gives  an overview of the basic functionality provided by the
  [5XGAP[105X  Character  Table Library. The main concepts and interface functions are
  presented  in  the  sections [14X2.1[114X  and  [14X2.2[114X,  Section [14X2.3[114X  shows  a few small
  examples.[133X
  
  [33X[0;0YIn order to force that the examples consist only of ASCII characters, we set
  the  user  preference  [10XDisplayFunction[110X of the [5XAtlasRep[105X to the value [10X"Print"[110X.
  This is necessary because the LaTeX and HTML versions of [5XGAPDoc[105X documents do
  not support non-ASCII characters.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xorigpref:= UserPreference( "AtlasRep", "DisplayFunction" );;[127X[104X
    [4X[25Xgap>[125X [27XSetUserPreference( "AtlasRep", "DisplayFunction", "Print" );[127X[104X
  [4X[32X[104X
  
  
  [1X2.1 [33X[0;0YConcepts used in the [5XGAP[105X[101X[1X Character Table Library[133X[101X
  
  [33X[0;0YThe main idea behind working with the [5XGAP[105X Character Table Library is to deal
  with  character  tables of groups but [13Xwithout[113X having access to these groups.
  This  situation  occurs  for  example  if  one extracts information from the
  printed [5XAtlas[105X of Finite Groups ([CCN+85]).[133X
  
  [33X[0;0YThis  restriction  means  first  of  all  that  we  need a way to access the
  character  tables,  see  Section [14X2.2[114X for that. Once we have such a character
  table, we can compute all those data about the underlying group [22XG[122X, say, that
  are  determined  by  the character table. Chapter [14X'Reference: Attributes and
  Properties  for  Groups  and  Character  Tables'[114X  lists  such attributes and
  properties.  For  example,  it can be computed from the character table of [22XG[122X
  whether [22XG[122X is solvable or not.[133X
  
  [33X[0;0YQuestions  that  cannot  be answered using only the character table of [22XG[122X can
  perhaps  be treated using additional information. For example, the structure
  of  subgroups of [22XG[122X is in general not determined by the character table of [22XG[122X,
  but  the  character table may yield partial information. Two examples can be
  found in the sections [14X2.3-4[114X and [14X2.3-6[114X.[133X
  
  [33X[0;0YIn the character table context, the role of homomorphisms between two groups
  is  taken  by  [13Xclass  fusions[113X. Monomorphisms correspond to subgroup fusions,
  epimorphisms  correspond  to factor fusions. Given two character tables of a
  group  [22XG[122X  and  a subgroup [22XH[122X of [22XG[122X, one can in general compute only [13Xcandidates[113X
  for  the  class  fusion  of [22XH[122X into [22XG[122X, for example using [2XPossibleClassFusions[102X
  ([14XReference:   PossibleClassFusions[114X).   Note   that  [22XG[122X  may  contain  several
  nonconjugate  subgroups  isomorphic  with  [22XH[122X, which may have different class
  fusions.[133X
  
  [33X[0;0YOne  can  often  reduce  a  question about a group [22XG[122X to a question about its
  maximal subgroups. In the character table context, it is often sufficient to
  know  the  character  table  of  [22XG[122X,  the  character  tables  of  its maximal
  subgroups,  and  their class fusions into [22XG[122X. We are in this situation if the
  attribute [2XMaxes[102X ([14X3.7-1[114X) is set in the character table of [22XG[122X.[133X
  
  [33X[0;0Y[13XSummary:[113X  The  character  theoretic  approach  that  is supported by the [5XGAP[105X
  Character  Table  Library, that is, an approach without explicitly using the
  underlying  groups,  has  the  advantages that it can be used to answer many
  questions,  and  that  these  computations  are  usually  cheap, compared to
  computations with groups. Disadvantages are that this approach is not always
  successful, and that answers are often [21Xnonconstructive[121X in the sense that one
  can show the existence of something without getting one's hands on it.[133X
  
  
  [1X2.2 [33X[0;0YAccessing a Character Table from the Library[133X[101X
  
  [33X[0;0YAs  stated  in Section [14X2.1[114X, we must define how character tables from the [5XGAP[105X
  Character Table Library can be accessed.[133X
  
  
  [1X2.2-1 [33X[0;0YAccessing a Character Table via a name[133X[101X
  
  [33X[0;0YThe most common way to access a character table from the [5XGAP[105X Character Table
  Library  is to call [2XCharacterTable[102X ([14X3.1-2[114X) with argument a string that is an
  [13Xadmissible  name[113X  for  the  character  table.  Typical  admissible names are
  similar  to the group names used in the [5XAtlas[105X of Finite Groups [CCN+85]. One
  of  these  names  is  the  [2XIdentifier[102X  ([14XReference:  Identifier for character
  tables[114X)  value  of  the  character  table,  this name is used by [5XGAP[105X when it
  prints library character tables.[133X
  
  [33X[0;0YFor  example, an admissible name for the character table of an almost simple
  group  is  the  [5XAtlas[105X name, such as [10XA5[110X, [10XM11[110X, or [10XL2(11).2[110X. Other names may be
  admissible,  for  example  [10XS6[110X  is  admissible for the symmetric group on six
  points, which is called [22XA_6.2_1[122X in the [5XAtlas[105X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XCharacterTable( "J1" );[127X[104X
    [4X[28XCharacterTable( "J1" )[128X[104X
    [4X[25Xgap>[125X [27XCharacterTable( "L2(11)" );[127X[104X
    [4X[28XCharacterTable( "L2(11)" )[128X[104X
    [4X[25Xgap>[125X [27XCharacterTable( "S5" );[127X[104X
    [4X[28XCharacterTable( "A5.2" )[128X[104X
  [4X[32X[104X
  
  
  [1X2.2-2 [33X[0;0YAccessing a Character Table via properties[133X[101X
  
  [33X[0;0YIf  one  does  not know an admissible name of the character table of a group
  one is interested in, or if one does not know whether ths character table is
  available  at  all,  one can use [2XAllCharacterTableNames[102X ([14X3.1-4[114X) to compute a
  list of identifiers of all available character tables with given properties.
  Analogously,  [2XOneCharacterTableName[102X  ([14X3.1-5[114X) can be used to compute one such
  identifier.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XAllCharacterTableNames( Size, 168 );[127X[104X
    [4X[28X[ "(2^2xD14):3", "2^3.7.3", "L3(2)", "L3(4)M7", "L3(4)M8" ][128X[104X
    [4X[25Xgap>[125X [27XOneCharacterTableName( NrConjugacyClasses, n -> n <= 4 );[127X[104X
    [4X[28X"S3"[128X[104X
  [4X[32X[104X
  
  [33X[0;0YFor  certain  filters, such as [2XSize[102X ([14XReference: Size[114X) and [2XNrConjugacyClasses[102X
  ([14XReference:  NrConjugacyClasses[114X),  the  computations  are  fast  because the
  values  for  all  library tables are precomputed. See [2XAllCharacterTableNames[102X
  ([14X3.1-4[114X) for an overview of these filters.[133X
  
  [33X[0;0YThe  function  [2XBrowseCTblLibInfo[102X ([14X3.5-2[114X) provides an interactive overview of
  available  character tables, which allows one for example to search also for
  substrings  in  identifiers  of character tables. This function is available
  only if the [5XBrowse[105X package has been loaded.[133X
  
  
  [1X2.2-3 [33X[0;0YAccessing a Character Table via a Table of Marks[133X[101X
  
  [33X[0;0YLet  [22XG[122X  be  a group whose table of marks is available via the [5XTomLib[105X package
  (see  [NMP18]  for how to access tables of marks from this library) then the
  [5XGAP[105X  Character  Table Library contains the character table of [22XG[122X, and one can
  access   this  table  by  using  the  table  of  marks  as  an  argument  of
  [2XCharacterTable[102X ([14X3.2-2[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xtom:= TableOfMarks( "M11" );[127X[104X
    [4X[28XTableOfMarks( "M11" )[128X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( tom );[127X[104X
    [4X[28XCharacterTable( "M11" )[128X[104X
  [4X[32X[104X
  
  
  [1X2.2-4 [33X[0;0YAccessing a Character Table relative to another Character Table[133X[101X
  
  [33X[0;0YIf  one  has  already a character table from the [5XGAP[105X Character Table Library
  that  belongs to the group [22XG[122X, say, then names of related tables can be found
  as follows.[133X
  
  [33X[0;0YThe  value  of  the  attribute  [2XMaxes[102X  ([14X3.7-1[114X),  if  known,  is  the list of
  identifiers  of  the character tables of all classes of maximal subgroups of
  [22XG[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "M11" );[127X[104X
    [4X[28XCharacterTable( "M11" )[128X[104X
    [4X[25Xgap>[125X [27XHasMaxes( t );[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XMaxes( t );[127X[104X
    [4X[28X[ "A6.2_3", "L2(11)", "3^2:Q8.2", "A5.2", "2.S4" ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YIf  the  [2XMaxes[102X ([14X3.7-1[114X) value of the character table with identifier [22Xid[122X, say,
  is known then the character table of the groups in the [22Xi[122X-th class of maximal
  subgroups can be accessed via the [21Xrelative name[121X [22Xid[122X[10XM[110X[22Xi[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XCharacterTable( "M11M2" );[127X[104X
    [4X[28XCharacterTable( "L2(11)" )[128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe    value    of    the    attribute    [2XNamesOfFusionSources[102X   ([14XReference:
  NamesOfFusionSources[114X)  is  the list of identifiers of those character tables
  which  store  class  fusions  to  [22XG[122X.  So  these  character  tables belong to
  subgroups of [22XG[122X and groups that have [22XG[122X as a factor group.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XNamesOfFusionSources( t );[127X[104X
    [4X[28X[ "A5.2", "A6.2_3", "P48/G1/L1/V1/ext2", "P48/G1/L1/V2/ext2", [128X[104X
    [4X[28X  "L2(11)", "2.S4", "3^5:M11", "3^6.M11", "s4", "3^2:Q8.2", "M11N2", [128X[104X
    [4X[28X  "5:4", "11:5" ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe    value    of    the    attribute    [2XComputedClassFusions[102X   ([14XReference:
  ComputedClassFusions[114X)  is  the list of records whose [10Xname[110X components are the
  identifiers  of those character tables to which class fusions are stored. So
  these character tables belong to overgroups and factor groups of [22XG[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XList( ComputedClassFusions( t ), r -> r.name );[127X[104X
    [4X[28X[ "A11", "M12", "M23", "HS", "McL", "ON", "3^5:M11", "B" ][128X[104X
  [4X[32X[104X
  
  
  [1X2.2-5 [33X[0;0YDifferent character tables for the same group[133X[101X
  
  [33X[0;0YThe  [5XGAP[105X  Character  Table  Library  may contain several different character
  tables  of  a given group, in the sense that the rows and columns are sorted
  differently.[133X
  
  [33X[0;0YFor  example, the [5XAtlas[105X table of the alternating group [22XA_5[122X is available, and
  since  [22XA_5[122X  is  isomorphic with the groups PSL[22X(2, 4)[122X and PSL[22X(2, 5)[122X, two more
  character  tables  of  [22XA_5[122X  can  be  constructed in a natural way. The three
  tables are of course permutation isomorphic. The first two are sorted in the
  same way, but the rows and columns of the third one are sorted differently.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt1:= CharacterTable( "A5" );;[127X[104X
    [4X[25Xgap>[125X [27Xt2:= CharacterTable( "PSL", 2, 4 );;[127X[104X
    [4X[25Xgap>[125X [27Xt3:= CharacterTable( "PSL", 2, 5 );;[127X[104X
    [4X[25Xgap>[125X [27XTransformingPermutationsCharacterTables( t1, t2 );[127X[104X
    [4X[28Xrec( columns := (), group := Group([ (4,5) ]), rows := () )[128X[104X
    [4X[25Xgap>[125X [27XTransformingPermutationsCharacterTables( t1, t3 );[127X[104X
    [4X[28Xrec( columns := (2,4)(3,5), group := Group([ (2,3) ]), [128X[104X
    [4X[28X  rows := (2,5,3,4) )[128X[104X
  [4X[32X[104X
  
  [33X[0;0YAnother  situation  where  several  character  tables for the same group are
  available  is  that  a  group contains several classes of isomorphic maximal
  subgroups such that the class fusions are different.[133X
  
  [33X[0;0YFor  example,  the  Mathieu  group  [22XM_12[122X  contains  two  classes  of maximal
  subgroups of index [22X12[122X, which are isomorphic with [22XM_11[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "M12" );[127X[104X
    [4X[28XCharacterTable( "M12" )[128X[104X
    [4X[25Xgap>[125X [27Xmx:= Maxes( t );[127X[104X
    [4X[28X[ "M11", "M12M2", "A6.2^2", "M12M4", "L2(11)", "3^2.2.S4", "M12M7", [128X[104X
    [4X[28X  "2xS5", "M8.S4", "4^2:D12", "A4xS3" ][128X[104X
    [4X[25Xgap>[125X [27Xs1:= CharacterTable( mx[1] );[127X[104X
    [4X[28XCharacterTable( "M11" )[128X[104X
    [4X[25Xgap>[125X [27Xs2:= CharacterTable( mx[2] );[127X[104X
    [4X[28XCharacterTable( "M12M2" )[128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe  class fusions into [22XM_12[122X are stored on the library tables of the maximal
  subgroups.  The  groups  in  the  first class of [22XM_11[122X type subgroups contain
  elements in the classes [10X4B[110X, [10X6B[110X, and [10X8B[110X of [22XM_12[122X, and the groups in the second
  class contain elements in the classes [10X4A[110X, [10X6A[110X, and [10X8A[110X. Note that according to
  the [5XAtlas[105X (see [CCN+85, p. 33]), the permutation characters of the action of
  [22XM_12[122X  on  the  cosets of [22XM_11[122X type subgroups from the two classes of maximal
  subgroups are [10X1a + 11a[110X and [10X1a + 11b[110X, respectively.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XGetFusionMap( s1, t );[127X[104X
    [4X[28X[ 1, 3, 4, 7, 8, 10, 12, 12, 15, 14 ][128X[104X
    [4X[25Xgap>[125X [27XGetFusionMap( s2, t );[127X[104X
    [4X[28X[ 1, 3, 4, 6, 8, 10, 11, 11, 14, 15 ][128X[104X
    [4X[25Xgap>[125X [27XDisplay( t );[127X[104X
    [4X[28XM12[128X[104X
    [4X[28X[128X[104X
    [4X[28X      2   6  4  6  1  2  5  5  1  2  1  3  3   1   .   .[128X[104X
    [4X[28X      3   3  1  1  3  2  .  .  .  1  1  .  .   .   .   .[128X[104X
    [4X[28X      5   1  1  .  .  .  .  .  1  .  .  .  .   1   .   .[128X[104X
    [4X[28X     11   1  .  .  .  .  .  .  .  .  .  .  .   .   1   1[128X[104X
    [4X[28X[128X[104X
    [4X[28X         1a 2a 2b 3a 3b 4a 4b 5a 6a 6b 8a 8b 10a 11a 11b[128X[104X
    [4X[28X     2P  1a 1a 1a 3a 3b 2b 2b 5a 3b 3a 4a 4b  5a 11b 11a[128X[104X
    [4X[28X     3P  1a 2a 2b 1a 1a 4a 4b 5a 2a 2b 8a 8b 10a 11a 11b[128X[104X
    [4X[28X     5P  1a 2a 2b 3a 3b 4a 4b 1a 6a 6b 8a 8b  2a 11a 11b[128X[104X
    [4X[28X    11P  1a 2a 2b 3a 3b 4a 4b 5a 6a 6b 8a 8b 10a  1a  1a[128X[104X
    [4X[28X[128X[104X
    [4X[28XX.1       1  1  1  1  1  1  1  1  1  1  1  1   1   1   1[128X[104X
    [4X[28XX.2      11 -1  3  2 -1 -1  3  1 -1  . -1  1  -1   .   .[128X[104X
    [4X[28XX.3      11 -1  3  2 -1  3 -1  1 -1  .  1 -1  -1   .   .[128X[104X
    [4X[28XX.4      16  4  . -2  1  .  .  1  1  .  .  .  -1   A  /A[128X[104X
    [4X[28XX.5      16  4  . -2  1  .  .  1  1  .  .  .  -1  /A   A[128X[104X
    [4X[28XX.6      45  5 -3  .  3  1  1  . -1  . -1 -1   .   1   1[128X[104X
    [4X[28XX.7      54  6  6  .  .  2  2 -1  .  .  .  .   1  -1  -1[128X[104X
    [4X[28XX.8      55 -5  7  1  1 -1 -1  .  1  1 -1 -1   .   .   .[128X[104X
    [4X[28XX.9      55 -5 -1  1  1  3 -1  .  1 -1 -1  1   .   .   .[128X[104X
    [4X[28XX.10     55 -5 -1  1  1 -1  3  .  1 -1  1 -1   .   .   .[128X[104X
    [4X[28XX.11     66  6  2  3  . -2 -2  1  . -1  .  .   1   .   .[128X[104X
    [4X[28XX.12     99 -1  3  .  3 -1 -1 -1 -1  .  1  1  -1   .   .[128X[104X
    [4X[28XX.13    120  . -8  3  .  .  .  .  .  1  .  .   .  -1  -1[128X[104X
    [4X[28XX.14    144  4  .  . -3  .  . -1  1  .  .  .  -1   1   1[128X[104X
    [4X[28XX.15    176 -4  . -4 -1  .  .  1 -1  .  .  .   1   .   .[128X[104X
    [4X[28X[128X[104X
    [4X[28XA = E(11)+E(11)^3+E(11)^4+E(11)^5+E(11)^9[128X[104X
    [4X[28X  = (-1+Sqrt(-11))/2 = b11[128X[104X
  [4X[32X[104X
  
  [33X[0;0YPermutation  equivalent  library  tables  are  related to each other. In the
  above  example,  the  table [10Xs2[110X is a [13Xduplicate[113X of [10Xs1[110X, and there are functions
  for making the relations explicit.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XIsDuplicateTable( s2 );[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XIdentifierOfMainTable( s2 );[127X[104X
    [4X[28X"M11"[128X[104X
    [4X[25Xgap>[125X [27XIdentifiersOfDuplicateTables( s1 );[127X[104X
    [4X[28X[ "HSM9", "M12M2", "ONM11" ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YSee Section [14X3.6[114X for details about duplicate character tables.[133X
  
  
  [1X2.3 [33X[0;0YExamples of Using the [5XGAP[105X[101X[1X Character Table Library[133X[101X
  
  [33X[0;0YThe   sections   [14X2.3-1[114X,   [14X2.3-2[114X,   and   [14X2.3-3[114X   show   how   the   function
  [2XAllCharacterTableNames[102X  ([14X3.1-4[114X)  can  be used to search for character tables
  with  certain  properties.  The [5XGAP[105X Character Table Library serves as a tool
  for finding and checking conjectures in these examples.[133X
  
  [33X[0;0YIn Section [14X2.3-6[114X, a question about a subgroup of the sporadic simple Fischer
  group  [22XG  =  Fi_23[122X  is  answered  using  only  character tables from the [5XGAP[105X
  Character Table Library.[133X
  
  [33X[0;0YMore examples can be found in [BGL+10], [Brea], [Bred], [Bree], [Bref].[133X
  
  
  [1X2.3-1 [33X[0;0YExample: Ambivalent Simple Groups[133X[101X
  
  [33X[0;0YA  group  [22XG[122X  is called [13Xambivalent[113X if each element in [22XG[122X is [22XG[122X-conjugate to its
  inverse.   Equivalently,   [22XG[122X   is  ambivalent  if  all  its  characters  are
  real-valued. We are interested in nonabelian simple ambivalent groups. Since
  ambivalence  is  of  course  invariant under permutation equivalence, we may
  omit duplicate character tables.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xisambivalent:= tbl -> PowerMap( tbl, -1 )[127X[104X
    [4X[25X>[125X [27X                           = [ 1 .. NrConjugacyClasses( tbl ) ];;[127X[104X
    [4X[25Xgap>[125X [27XAllCharacterTableNames( IsSimple, true, IsDuplicateTable, false,[127X[104X
    [4X[25X>[125X [27X       IsAbelian, false, isambivalent, true );[127X[104X
    [4X[28X[ "3D4(2)", "3D4(3)", "3D4(4)", "A10", "A14", "A5", "A6", "J1", "J2", [128X[104X
    [4X[28X  "L2(101)", "L2(109)", "L2(113)", "L2(121)", "L2(125)", "L2(13)", [128X[104X
    [4X[28X  "L2(16)", "L2(17)", "L2(25)", "L2(29)", "L2(32)", "L2(37)", [128X[104X
    [4X[28X  "L2(41)", "L2(49)", "L2(53)", "L2(61)", "L2(64)", "L2(73)", [128X[104X
    [4X[28X  "L2(8)", "L2(81)", "L2(89)", "L2(97)", "O12+(2)", "O12-(2)", [128X[104X
    [4X[28X  "O12-(3)", "O7(5)", "O8+(2)", "O8+(3)", "O8+(7)", "O8-(2)", [128X[104X
    [4X[28X  "O8-(3)", "O9(3)", "S10(2)", "S12(2)", "S4(4)", "S4(5)", "S4(8)", [128X[104X
    [4X[28X  "S4(9)", "S6(2)", "S6(4)", "S6(5)", "S8(2)" ][128X[104X
  [4X[32X[104X
  
  
  [1X2.3-2 [33X[0;0YExample: Simple [22Xp[122X[101X[1X-pure Groups[133X[101X
  
  [33X[0;0YA  group  [22XG[122X  is  called [13X[22Xp[122X-pure[113X for a prime integer [22Xp[122X that divides [22X|G|[122X if the
  centralizer   orders   of   nonidentity   [22Xp[122X-elements   in  [22XG[122X  are  [22Xp[122X-powers.
  Equivalently,  [22XG[122X  is  [22Xp[122X-pure if [22Xp[122X divides [22X|G|[122X and each element in [22XG[122X of order
  divisible  by [22Xp[122X is a [22Xp[122X-element. (This property was studied by L. Héthelyi in
  2002.)[133X
  
  [33X[0;0YWe are interested in small nonabelian simple [22Xp[122X-pure groups.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xisppure:= function( p )[127X[104X
    [4X[25X>[125X [27X     return tbl -> Size( tbl ) mod p = 0 and[127X[104X
    [4X[25X>[125X [27X       ForAll( OrdersClassRepresentatives( tbl ),[127X[104X
    [4X[25X>[125X [27X               n -> n mod p <> 0 or IsPrimePowerInt( n ) );[127X[104X
    [4X[25X>[125X [27X   end;;[127X[104X
    [4X[25Xgap>[125X [27Xfor i in [ 2, 3, 5, 7, 11, 13 ] do[127X[104X
    [4X[25X>[125X [27X     Print( i, "\n",[127X[104X
    [4X[25X>[125X [27X       AllCharacterTableNames( IsSimple, true, IsAbelian, false,[127X[104X
    [4X[25X>[125X [27X           IsDuplicateTable, false, isppure( i ), true ),[127X[104X
    [4X[25X>[125X [27X       "\n" );[127X[104X
    [4X[25X>[125X [27X   od;[127X[104X
    [4X[28X2[128X[104X
    [4X[28X[ "A5", "A6", "L2(16)", "L2(17)", "L2(31)", "L2(32)", "L2(64)", [128X[104X
    [4X[28X  "L2(8)", "L3(2)", "L3(4)", "Sz(32)", "Sz(8)" ][128X[104X
    [4X[28X3[128X[104X
    [4X[28X[ "A5", "A6", "L2(17)", "L2(19)", "L2(27)", "L2(53)", "L2(8)", [128X[104X
    [4X[28X  "L2(81)", "L3(2)", "L3(4)" ][128X[104X
    [4X[28X5[128X[104X
    [4X[28X[ "A5", "A6", "A7", "L2(11)", "L2(125)", "L2(25)", "L2(49)", "L3(4)", [128X[104X
    [4X[28X  "M11", "M22", "S4(7)", "Sz(32)", "Sz(8)", "U4(2)", "U4(3)" ][128X[104X
    [4X[28X7[128X[104X
    [4X[28X[ "A7", "A8", "A9", "G2(3)", "HS", "J1", "J2", "L2(13)", "L2(49)", [128X[104X
    [4X[28X  "L2(8)", "L2(97)", "L3(2)", "L3(4)", "M22", "O8+(2)", "S6(2)", [128X[104X
    [4X[28X  "Sz(8)", "U3(3)", "U3(5)", "U4(3)", "U6(2)" ][128X[104X
    [4X[28X11[128X[104X
    [4X[28X[ "A11", "A12", "A13", "Co2", "HS", "J1", "L2(11)", "L2(121)", [128X[104X
    [4X[28X  "L2(23)", "L5(3)", "M11", "M12", "M22", "M23", "M24", "McL", [128X[104X
    [4X[28X  "O10+(3)", "O12+(3)", "ON", "Suz", "U5(2)", "U6(2)" ][128X[104X
    [4X[28X13[128X[104X
    [4X[28X[ "2E6(2)", "2F4(2)'", "3D4(2)", "A13", "A14", "A15", "F4(2)", [128X[104X
    [4X[28X  "Fi22", "G2(3)", "G2(4)", "L2(13)", "L2(25)", "L2(27)", "L3(3)", [128X[104X
    [4X[28X  "L4(3)", "O7(3)", "O8+(3)", "S4(5)", "S6(3)", "Suz", "Sz(8)", [128X[104X
    [4X[28X  "U3(4)" ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YLooking  at these examples, we may observe that the alternating group [22XA_n[122X of
  degree  [22Xn[122X  is [22X2[122X-pure iff [22Xn ∈ { 4, 5, 6 }[122X, [22X3[122X-pure iff [22Xn ∈ { 3, 4, 5, 6 }[122X, and
  [22Xp[122X-pure, for [22Xp ≥ 5[122X, iff [22Xn ∈ { p, p+1, p+2 }[122X.[133X
  
  [33X[0;0YAlso,  the  Suzuki  groups  [22XSz(q)[122X  are  [22X2[122X-pure  since  the  centralizers  of
  nonidentity [22X2[122X-elements are contained in Sylow [22X2[122X-subgroups.[133X
  
  [33X[0;0YFrom  the  inspection of the generic character table(s) of [22XPSL(2, q)[122X, we see
  that  [22XPSL(2,  p^d)[122X  is  [22Xp[122X-pure  Additionally, exactly the following cases of
  [22Xl[122X-purity occur, for a prime [22Xl[122X.[133X
  
  [30X    [33X[0;6Y[22Xq[122X is even and [22Xq-1[122X or [22Xq+1[122X is a power of [22Xl[122X.[133X
  
  [30X    [33X[0;6YFor [22Xq ≡ 1 mod 4[122X, [22X(q+1)/2[122X is a power of [22Xl[122X or [22Xq-1[122X is a power of [22Xl = 2[122X.[133X
  
  [30X    [33X[0;6YFor [22Xq ≡ 3 mod 4[122X, [22X(q-1)/2[122X is a power of [22Xl[122X or [22Xq+1[122X is a power of [22Xl = 2[122X.[133X
  
  
  [1X2.3-3 [33X[0;0YExample: Simple Groups with only one [22Xp[122X[101X[1X-Block[133X[101X
  
  [33X[0;0YAre there nonabelian simple groups with only one [22Xp[122X-block, for some prime [22Xp[122X?[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xfun:= function( tbl )[127X[104X
    [4X[25X>[125X [27X     local result, p, bl;[127X[104X
    [4X[25X>[125X [27X[127X[104X
    [4X[25X>[125X [27X     result:= false;[127X[104X
    [4X[25X>[125X [27X     for p in PrimeDivisors( Size( tbl ) ) do[127X[104X
    [4X[25X>[125X [27X       bl:= PrimeBlocks( tbl, p );[127X[104X
    [4X[25X>[125X [27X       if Length( bl.defect ) = 1 then[127X[104X
    [4X[25X>[125X [27X         result:= true;[127X[104X
    [4X[25X>[125X [27X         Print( "only one block: ", Identifier( tbl ), ", p = ", p, "\n" );[127X[104X
    [4X[25X>[125X [27X       fi;[127X[104X
    [4X[25X>[125X [27X     od;[127X[104X
    [4X[25X>[125X [27X[127X[104X
    [4X[25X>[125X [27X     return result;[127X[104X
    [4X[25X>[125X [27Xend;;[127X[104X
    [4X[25Xgap>[125X [27XAllCharacterTableNames( IsSimple, true, IsAbelian, false,[127X[104X
    [4X[25X>[125X [27X                           IsDuplicateTable, false, fun, true );[127X[104X
    [4X[28Xonly one block: M22, p = 2[128X[104X
    [4X[28Xonly one block: M24, p = 2[128X[104X
    [4X[28X[ "M22", "M24" ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YWe see that the sporadic simple groups [22XM_22[122X and [22XM_24[122X have only one [22X2[122X-block.[133X
  
  
  [1X2.3-4 [33X[0;0YExample:The Sylow [22X3[122X[101X[1X subgroup of [22X3.O'N[122X[101X[1X[133X[101X
  
  [33X[0;0YWe  want  to  determine the structure of the Sylow [22X3[122X-subgroups of the triple
  cover [22XG = 3.O'N[122X of the sporadic simple O'Nan group [22XO'N[122X. The Sylow [22X3[122X-subgroup
  of  [22XO'N[122X  is  an  elementary  abelian  group  of order [22X3^4[122X, since the Sylow [22X3[122X
  normalizer in [22XO'N[122X has the structure [22X3^4:2^1+4D_10[122X (see [CCN+85, p. 132]).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XCharacterTable( "ONN3" );[127X[104X
    [4X[28XCharacterTable( "3^4:2^(1+4)D10" )[128X[104X
  [4X[32X[104X
  
  [33X[0;0YLet  [22XP[122X  be  a  Sylow  [22X3[122X-subgroup  of  [22XG[122X.  Then  [22XP[122X  is not abelian, since the
  centralizer order of any preimage of an element of order three in the simple
  factor  group  of  [22XG[122X is not divisible by [22X3^5[122X. Moreover, the exponent of [22XP[122X is
  three.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27X3t:= CharacterTable( "3.ON" );;[127X[104X
    [4X[25Xgap>[125X [27Xorders:= OrdersClassRepresentatives( 3t );;[127X[104X
    [4X[25Xgap>[125X [27Xord3:= PositionsProperty( orders, x -> x = 3 );[127X[104X
    [4X[28X[ 2, 3, 7 ][128X[104X
    [4X[25Xgap>[125X [27Xsizes:= SizesCentralizers( 3t ){ ord3 };[127X[104X
    [4X[28X[ 1382446517760, 1382446517760, 3240 ][128X[104X
    [4X[25Xgap>[125X [27XSize( 3t );[127X[104X
    [4X[28X1382446517760[128X[104X
    [4X[25Xgap>[125X [27XCollected( Factors( sizes[3] ) );[127X[104X
    [4X[28X[ [ 2, 3 ], [ 3, 4 ], [ 5, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27X9 in orders;[127X[104X
    [4X[28Xfalse[128X[104X
  [4X[32X[104X
  
  [33X[0;0YSo both the centre and the Frattini subgroup of [22XP[122X are equal to the centre of
  [22XG[122X, hence [22XP[122X is an extraspecial group [22X3^1+4_+[122X.[133X
  
  
  [1X2.3-5 [33X[0;0YExample: Primitive Permutation Characters of [22X2.A_6[122X[101X[1X[133X[101X
  
  [33X[0;0YIt is often interesting to compute the primitive permutation characters of a
  group  [22XG[122X,  that  is,  the  characters of the permutation actions of [22XG[122X on the
  cosets  of  its  maximal  subgroups.  These  characters  can be computed for
  example  when the character tables of [22XG[122X, the character tables of its maximal
  subgroups,  and the class fusions from these character tables into the table
  of [22XG[122X are known.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xtbl:= CharacterTable( "2.A6" );;[127X[104X
    [4X[25Xgap>[125X [27XHasMaxes( tbl );[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xmaxes:= Maxes( tbl );[127X[104X
    [4X[28X[ "2.A5", "2.A6M2", "3^2:8", "2.Symm(4)", "2.A6M5" ][128X[104X
    [4X[25Xgap>[125X [27Xmx:= List( maxes, CharacterTable );;[127X[104X
    [4X[25Xgap>[125X [27Xprim1:= List( mx, s -> TrivialCharacter( s )^tbl );;[127X[104X
    [4X[25Xgap>[125X [27XDisplay( tbl,[127X[104X
    [4X[25X>[125X [27X     rec( chars:= prim1, centralizers:= false, powermap:= false ) );[127X[104X
    [4X[28X2.A6[128X[104X
    [4X[28X[128X[104X
    [4X[28X       1a 2a 4a 3a 6a 3b 6b 8a 8b 5a 10a 5b 10b[128X[104X
    [4X[28X[128X[104X
    [4X[28XY.1     6  6  2  3  3  .  .  .  .  1   1  1   1[128X[104X
    [4X[28XY.2     6  6  2  .  .  3  3  .  .  1   1  1   1[128X[104X
    [4X[28XY.3    10 10  2  1  1  1  1  2  2  .   .  .   .[128X[104X
    [4X[28XY.4    15 15  3  3  3  .  .  1  1  .   .  .   .[128X[104X
    [4X[28XY.5    15 15  3  .  .  3  3  1  1  .   .  .   .[128X[104X
  [4X[32X[104X
  
  [33X[0;0YThese permutation characters are the ones listed in [CCN+85, p. 4].[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XPermCharInfo( tbl, prim1 ).ATLAS;[127X[104X
    [4X[28X[ "1a+5a", "1a+5b", "1a+9a", "1a+5a+9a", "1a+5b+9a" ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YAlternatively, one can compute the primitive permutation characters from the
  table of marks if this table and the fusion into it are known.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xtom:= TableOfMarks( tbl );[127X[104X
    [4X[28XTableOfMarks( "2.A6" )[128X[104X
    [4X[25Xgap>[125X [27Xallperm:= PermCharsTom( tbl, tom );;[127X[104X
    [4X[25Xgap>[125X [27Xprim2:= allperm{ MaximalSubgroupsTom( tom )[1] };;[127X[104X
    [4X[25Xgap>[125X [27XDisplay( tbl,[127X[104X
    [4X[25X>[125X [27X     rec( chars:= prim2, centralizers:= false, powermap:= false ) );[127X[104X
    [4X[28X2.A6[128X[104X
    [4X[28X[128X[104X
    [4X[28X       1a 2a 4a 3a 6a 3b 6b 8a 8b 5a 10a 5b 10b[128X[104X
    [4X[28X[128X[104X
    [4X[28XY.1     6  6  2  3  3  .  .  .  .  1   1  1   1[128X[104X
    [4X[28XY.2     6  6  2  .  .  3  3  .  .  1   1  1   1[128X[104X
    [4X[28XY.3    10 10  2  1  1  1  1  2  2  .   .  .   .[128X[104X
    [4X[28XY.4    15 15  3  .  .  3  3  1  1  .   .  .   .[128X[104X
    [4X[28XY.5    15 15  3  3  3  .  .  1  1  .   .  .   .[128X[104X
  [4X[32X[104X
  
  [33X[0;0YWe  see  that  the two approaches yield the same permutation characters, but
  the  two  lists are sorted in a different way. The latter is due to the fact
  that  the  rows  of  the  table  of  marks  are ordered in a way that is not
  compatible  with  the ordering of maximal subgroups for the character table.
  Moreover,  there  is no way to choose the fusion from the character table to
  the  table  of  marks  in  such  a  way  that  the  two lists of permutation
  characters would become equal. The component [10Xperm[110X in the [2XFusionToTom[102X ([14X3.2-4[114X)
  record of the character table describes the incompatibility.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XFusionToTom( tbl );[127X[104X
    [4X[28Xrec( map := [ 1, 2, 5, 4, 8, 3, 7, 11, 11, 6, 13, 6, 13 ], [128X[104X
    [4X[28X  name := "2.A6", perm := (4,5), [128X[104X
    [4X[28X  text := "fusion map is unique up to table autom." )[128X[104X
  [4X[32X[104X
  
  
  [1X2.3-6 [33X[0;0YExample: A Permutation Character of [22XFi_23[122X[101X[1X[133X[101X
  
  [33X[0;0YLet  [22Xx[122X  be  a [10X3B[110X element in the sporadic simple Fischer group [22XG = Fi_23[122X. The
  normalizer   [22XM[122X   of   [22Xx[122X   in   [22XG[122X   is   a   maximal  subgroup  of  the  type
  [22X3^{1+8}_+.2^{1+6}_-.3^{1+2}_+.2S_4[122X. We are interested in the distribution of
  the  elements  of  the  normal  subgroup [22XN[122X of the type [22X3^{1+8}_+[122X in [22XM[122X to the
  conjugacy classes of [22XG[122X.[133X
  
  [33X[0;0YThis  information  can be computed from the permutation character [22Xπ = 1_N^G[122X,
  so  we try to compute this permutation character. We have [22Xπ = (1_N^M)^G[122X, and
  [22X1_N^M[122X  can  be  computed  as  the  inflation of the regular character of the
  factor  group  [22XM/N[122X  to  [22XM[122X.  Note  that  the  character tables of [22XG[122X and [22XM[122X are
  available,  as well as the class fusion of [22XM[122X in [22XG[122X, and that [22XN[122X is the largest
  normal [22X3[122X-subgroup of [22XM[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "Fi23" );[127X[104X
    [4X[28XCharacterTable( "Fi23" )[128X[104X
    [4X[25Xgap>[125X [27Xmx:= Maxes( t );[127X[104X
    [4X[28X[ "2.Fi22", "O8+(3).3.2", "2^2.U6(2).2", "S8(2)", "S3xO7(3)", [128X[104X
    [4X[28X  "2..11.m23", "3^(1+8).2^(1+6).3^(1+2).2S4", "Fi23M8", "A12.2", [128X[104X
    [4X[28X  "(2^2x2^(1+8)).(3xU4(2)).2", "2^(6+8):(A7xS3)", "S4xS6(2)", [128X[104X
    [4X[28X  "S4(4).4", "L2(23)" ][128X[104X
    [4X[25Xgap>[125X [27Xm:= CharacterTable( mx[7] );[127X[104X
    [4X[28XCharacterTable( "3^(1+8).2^(1+6).3^(1+2).2S4" )[128X[104X
    [4X[25Xgap>[125X [27Xn:= ClassPositionsOfPCore( m, 3 );[127X[104X
    [4X[28X[ 1 .. 6 ][128X[104X
    [4X[25Xgap>[125X [27Xf:= m / n;[127X[104X
    [4X[28XCharacterTable( "3^(1+8).2^(1+6).3^(1+2).2S4/[ 1, 2, 3, 4, 5, 6 ]" )[128X[104X
    [4X[25Xgap>[125X [27Xreg:= 0 * [ 1 .. NrConjugacyClasses( f ) ];;[127X[104X
    [4X[25Xgap>[125X [27Xreg[1]:= Size( f );;[127X[104X
    [4X[25Xgap>[125X [27Xinfl:= reg{ GetFusionMap( m, f ) };[127X[104X
    [4X[28X[ 165888, 165888, 165888, 165888, 165888, 165888, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ][128X[104X
    [4X[25Xgap>[125X [27Xind:= Induced( m, t, [ infl ] );[127X[104X
    [4X[28X[ ClassFunction( CharacterTable( "Fi23" ),[128X[104X
    [4X[28X  [ 207766624665600, 0, 0, 0, 603832320, 127567872, 6635520, 663552, [128X[104X
    [4X[28X      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X      0, 0, 0, 0, 0, 0 ] ) ][128X[104X
    [4X[25Xgap>[125X [27XPermCharInfo( t, ind ).contained;[127X[104X
    [4X[28X[ [ 1, 0, 0, 0, 864, 1538, 3456, 13824, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, [128X[104X
    [4X[28X      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ] ][128X[104X
    [4X[25Xgap>[125X [27XPositionsProperty( OrdersClassRepresentatives( t ), x -> x = 3 );[127X[104X
    [4X[28X[ 5, 6, 7, 8 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThus [22XN[122X contains [22X864[122X elements in the class [10X3A[110X, [22X1538[122X elements in the class [10X3B[110X,
  and so on.[133X
  
  
  [1X2.3-7 [33X[0;0YExample: Non-commutators in the commutator group[133X[101X
  
  [33X[0;0YIn general, not every element in the commutator group of a group is itself a
  commutator.  Are  there examples in the Character Table Library, and if yes,
  what is a smallest one?[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xnam:= OneCharacterTableName( CommutatorLength, x -> x > 1[127X[104X
    [4X[25X>[125X [27X                                : OrderedBy:= Size );[127X[104X
    [4X[28X"3.(A4x3):2"[128X[104X
    [4X[25Xgap>[125X [27XSize( CharacterTable( nam ) );[127X[104X
    [4X[28X216[128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe smallest groups with this property have order [22X96[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XOneSmallGroup( Size, [ 2 .. 100 ],[127X[104X
    [4X[25X>[125X [27X                  G -> CommutatorLength( G ) > 1, true );[127X[104X
    [4X[28X<pc group of size 96 with 6 generators>[128X[104X
  [4X[32X[104X
  
  [33X[0;0Y(Note the different syntax: [2XOneSmallGroup[102X ([14Xsmallgrp: OneSmallGroup[114X) does not
  admit a function such as [10Xx -> x > 1[110X for describing the admissible values.)[133X
  
  [33X[0;0YNonabelian  simple groups cannot be expected to have non-commutators, by the
  main theorem in [LOST10].[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XOneCharacterTableName( IsSimple, true, IsAbelian, false,[127X[104X
    [4X[25X>[125X [27X                          IsDuplicateTable, false,[127X[104X
    [4X[25X>[125X [27X                          CommutatorLength, x -> x > 1[127X[104X
    [4X[25X>[125X [27X                          : OrderedBy:= Size );[127X[104X
    [4X[28Xfail[128X[104X
  [4X[32X[104X
  
  [33X[0;0YPerfect groups can contain non-commutators.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xnam:= OneCharacterTableName( IsPerfect, true,[127X[104X
    [4X[25X>[125X [27X                                IsDuplicateTable, false,[127X[104X
    [4X[25X>[125X [27X                                CommutatorLength, x -> x > 1[127X[104X
    [4X[25X>[125X [27X                                : OrderedBy:= Size );[127X[104X
    [4X[28X"P1/G1/L1/V1/ext2"[128X[104X
    [4X[25Xgap>[125X [27XSize( CharacterTable( nam ) );[127X[104X
    [4X[28X960[128X[104X
  [4X[32X[104X
  
  [33X[0;0YThis  is  in  fact  the  smallest  example  of a perfect group that contains
  non-commutators.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xfor n in [ 2 .. 960 ] do[127X[104X
    [4X[25X>[125X [27X     for i in [ 1 .. NrPerfectGroups( n ) ] do[127X[104X
    [4X[25X>[125X [27X       g:= PerfectGroup( n,  i);[127X[104X
    [4X[25X>[125X [27X       if CommutatorLength( g ) <> 1 then[127X[104X
    [4X[25X>[125X [27X         Print( [ n, i ], "\n" );[127X[104X
    [4X[25X>[125X [27X       fi;[127X[104X
    [4X[25X>[125X [27X     od;[127X[104X
    [4X[25X>[125X [27X   od;[127X[104X
    [4X[28X[ 960, 2 ][128X[104X
  [4X[32X[104X
  
  
  [1X2.3-8 [33X[0;0YExample: An irreducible [22X11[122X[101X[1X-modular character of [22XJ_4[122X[101X[1X (December 2018)[133X[101X
  
  [33X[0;0YLet  [22XG[122X  be the sporadic simple Janko group [22XJ_4[122X. For the ordinary irreducible
  characters  of  degree  [22X1333[122X  of [22XG[122X, the reductions modulo [22X11[122X are known to be
  irreducible Brauer characters.[133X
  
  [33X[0;0YDavid Craven asked Richard Parker how to show that the antisymmetric squares
  of these Brauer characters are irreducible. Richard proposed the following.[133X
  
  [33X[0;0YRestrict  the  given ordinary character [22Xχ[122X, say, to a subgroup [22XS[122X of [22XJ_4[122X whose
  [22X11[122X-modular  character  table  is  known,  decompose the restriction [22Xχ_S[122X into
  irreducible  Brauer  characters,  and  compute  those  constituents that are
  constant on all subsets of conjugacy classes that fuse in [22XJ_4[122X. If the Brauer
  character [22Xχ_S[122X cannot be written as a sum of two such constituents then [22Xχ[122X, as
  a Brauer character of [22XJ_4[122X, is irreducible.[133X
  
  [33X[0;0YHere is a [5XGAP[105X session that shows how to apply this idea.[133X
  
  [33X[0;0YThe  group  [22XJ_4[122X  has  exactly  two ordinary irreducible characters of degree
  [22X1333[122X.  They  are  complex conjugate, and so are their antisymmetric squares.
  Thus we may consider just one of the two.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "J4" );;[127X[104X
    [4X[25Xgap>[125X [27Xdeg1333:= Filtered( Irr( t ), x -> x[1] = 1333 );;[127X[104X
    [4X[25Xgap>[125X [27Xantisym:= AntiSymmetricParts( t, deg1333, 2 );;[127X[104X
    [4X[25Xgap>[125X [27XList(  antisym, x -> Position( Irr( t ), x ) );[127X[104X
    [4X[28X[ 7, 6 ][128X[104X
    [4X[25Xgap>[125X [27XComplexConjugate( antisym[1] ) = antisym[2];[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xchi:= antisym[1];;  chi[1];[127X[104X
    [4X[28X887778[128X[104X
  [4X[32X[104X
  
  [33X[0;0YLet  [22XS[122X be a maximal subgroup of the structure [22X2^11:M_24[122X in [22XJ_4[122X. Fortunately,
  the [22X11[122X-modular character table of [22XS[122X is available (it had been constructed by
  Christoph  Jansen),  and  we  can restrict the interesting character to this
  table.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xs:= CharacterTable( Maxes( t )[1] );;[127X[104X
    [4X[25Xgap>[125X [27XSize( s ) = 2^11 * Size( CharacterTable( "M24" ) );[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xrest:= RestrictedClassFunction( chi, s );;[127X[104X
    [4X[25Xgap>[125X [27Xsmod11:= s mod 11;;[127X[104X
    [4X[25Xgap>[125X [27Xrest:= RestrictedClassFunction( rest, smod11 );;[127X[104X
  [4X[32X[104X
  
  [33X[0;0YThe  restriction  is  a  sum  of  nine pairwise different irreducible Brauer
  characters of [22XS[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xdec:= Decomposition( Irr( smod11 ), [ rest ], "nonnegative" )[1];;[127X[104X
    [4X[25Xgap>[125X [27XSum( dec );[127X[104X
    [4X[28X9[128X[104X
    [4X[25Xgap>[125X [27Xconstpos:= PositionsProperty( dec, x -> x <> 0 );[127X[104X
    [4X[28X[ 15, 36, 46, 53, 55, 58, 63, 67, 69 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YNext we compute those sets of classes of [22XS[122X which fuse in [22XJ_4[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xsmod11fuss:= GetFusionMap( smod11, s );;[127X[104X
    [4X[25Xgap>[125X [27Xsfust:= GetFusionMap( s, t );;[127X[104X
    [4X[25Xgap>[125X [27Xfus:= CompositionMaps( sfust, smod11fuss );;[127X[104X
    [4X[25Xgap>[125X [27Xinv:= Filtered( InverseMap( fus ), IsList );[127X[104X
    [4X[28X[ [ 3, 4, 5 ], [ 2, 6, 7 ], [ 8, 9 ], [ 10, 11, 16 ], [128X[104X
    [4X[28X  [ 12, 14, 15, 17, 18, 21 ], [ 13, 19, 20, 22 ], [ 26, 27, 28, 30 ], [128X[104X
    [4X[28X  [ 25, 29, 31 ], [ 34, 39 ], [ 35, 37, 38 ], [ 40, 42 ], [ 41, 43 ], [128X[104X
    [4X[28X  [ 44, 47, 48 ], [ 45, 49, 50 ], [ 46, 51 ], [ 56, 57 ], [ 63, 64 ], [128X[104X
    [4X[28X  [ 69, 70 ] ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YFinally, we run over all [22X2^9[122X subsets of the irreducible constituents.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xconst:= Irr( smod11 ){ constpos };;[127X[104X
    [4X[25Xgap>[125X [27Xzero:= 0 * TrivialCharacter( smod11 );;[127X[104X
    [4X[25Xgap>[125X [27Xcomb:= List( Combinations( const ), x -> Sum( x, zero ) );;[127X[104X
    [4X[25Xgap>[125X [27Xcand:= Filtered( comb,[127X[104X
    [4X[25X>[125X [27X              x -> ForAll( inv, l -> Length( Set( x{ l } ) ) = 1 ) );;[127X[104X
    [4X[25Xgap>[125X [27XList( cand, x -> x[1] );[127X[104X
    [4X[28X[ 0, 887778 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YWe  see  that no proper subset of the constituents yields a Brauer character
  that can be restricted from [22XJ_4[122X.[133X
  
  
  [1X2.3-9  [33X[0;0YExample:  Tensor  Products  that are Generalized Projectives (October[101X
  [1X2019)[133X[101X
  
  [33X[0;0YLet  [22XG[122X  be a finite group and [22Xp[122X be a prime integer. If the tensor product [22XΦ[122X,
  say,  of two ordinary irreducible characters of [22XG[122X vanishes on all [22Xp[122X-singular
  elements   of  [22XG[122X  then  [22XΦ[122X  is  a  [22Xℤ[122X-linear  combination  of  the  [13Xprojective
  indecomposable  characters[113X [22XΦ_φ = ∑_{χ ∈ Irr(G)} d_{χ φ} χ[122X of [22XG[122X, where [22Xφ[122X runs
  over  the  irreducible  [22Xp[122X-modular  Brauer characters of [22XG[122X and [22Xd_{χ φ}[122X is the
  decomposition  number  of [22Xχ[122X and [22Xφ[122X. (See for example [Nav98, p. 25] or [LP10,
  Def.  4.3.1].)  Such  class  functions  are  called  generalized  projective
  characters.[133X
  
  [33X[0;0YIn  fact,  very often [22XΦ[122X is a projective character, that is, the coefficients
  of   the   decomposition   into  projective  indecomposable  characters  are
  nonnegative.[133X
  
  [33X[0;0YWe are interested in examples where this is [13Xnot[113X the case. For that, we write
  a  small  [5XGAP[105X function that computes, for a given [22Xp[122X-modular character table,
  those   tensor   products   of  ordinary  irreducible  characters  that  are
  generalized projective characters but are not projective.[133X
  
  [33X[0;0YMany  years  ago, Richard Parker had been interested in the question whether
  such  tensor  products can exist for a given group. Note that forming tensor
  products  that  vanish  on  [22Xp[122X-singular  elements  is  a  recipe for creating
  projective  characters,  provided  one  knows  in advance that the answer is
  negative for the given group.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XGenProjNotProj:= function( modtbl )[127X[104X
    [4X[25X>[125X [27X     local p, tbl, X, PIMs, n, psingular, list, labels, i, j, psi,[127X[104X
    [4X[25X>[125X [27X           pos, dec, poss;[127X[104X
    [4X[25X>[125X [27X[127X[104X
    [4X[25X>[125X [27X     p:= UnderlyingCharacteristic( modtbl );[127X[104X
    [4X[25X>[125X [27X     tbl:= OrdinaryCharacterTable( modtbl );[127X[104X
    [4X[25X>[125X [27X     X:= Irr( tbl );[127X[104X
    [4X[25X>[125X [27X     PIMs:= TransposedMat( DecompositionMatrix( modtbl ) ) * X;[127X[104X
    [4X[25X>[125X [27X     n:= Length( X );[127X[104X
    [4X[25X>[125X [27X     psingular:= Difference( [ 1 .. n ], GetFusionMap( modtbl, tbl ) );[127X[104X
    [4X[25X>[125X [27X     list:= [];[127X[104X
    [4X[25X>[125X [27X     labels:= [];[127X[104X
    [4X[25X>[125X [27X     for i in [ 1 .. n ] do[127X[104X
    [4X[25X>[125X [27X       for j in [ 1 .. i ] do[127X[104X
    [4X[25X>[125X [27X         psi:= List( [ 1 .. n ], x -> X[i][x] * X[j][x] );[127X[104X
    [4X[25X>[125X [27X         if IsZero( psi{ psingular } ) then[127X[104X
    [4X[25X>[125X [27X           # This is a generalized projective character.[127X[104X
    [4X[25X>[125X [27X           pos:= Position( list, psi );[127X[104X
    [4X[25X>[125X [27X           if pos = fail then[127X[104X
    [4X[25X>[125X [27X             Add( list, psi );[127X[104X
    [4X[25X>[125X [27X             Add( labels, [ [ j, i ] ] );[127X[104X
    [4X[25X>[125X [27X           else[127X[104X
    [4X[25X>[125X [27X             Add( labels[ pos ], [ j, i ] );[127X[104X
    [4X[25X>[125X [27X           fi;[127X[104X
    [4X[25X>[125X [27X         fi;[127X[104X
    [4X[25X>[125X [27X       od;[127X[104X
    [4X[25X>[125X [27X     od;[127X[104X
    [4X[25X>[125X [27X[127X[104X
    [4X[25X>[125X [27X     if Length( list ) > 0 then[127X[104X
    [4X[25X>[125X [27X       # Decompose the generalized projective tensor products[127X[104X
    [4X[25X>[125X [27X       # into the projective indecomposables.[127X[104X
    [4X[25X>[125X [27X       dec:= Decomposition( PIMs, list, "nonnegative" );[127X[104X
    [4X[25X>[125X [27X       poss:= Positions( dec, fail );[127X[104X
    [4X[25X>[125X [27X       return Set( Concatenation( labels{ poss } ) );[127X[104X
    [4X[25X>[125X [27X     else[127X[104X
    [4X[25X>[125X [27X       return [];[127X[104X
    [4X[25X>[125X [27X     fi;[127X[104X
    [4X[25X>[125X [27X     end;;[127X[104X
  [4X[32X[104X
  
  [33X[0;0YOne  group  for which the function returns a nonempty result is the sporadic
  simple Janko group [22XJ_2[122X in characteristic [22X2[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xtbl:= CharacterTable( "J2" );;[127X[104X
    [4X[25Xgap>[125X [27Xmodtbl:= tbl mod 2;;[127X[104X
    [4X[25Xgap>[125X [27Xpairs:= GenProjNotProj( modtbl );[127X[104X
    [4X[28X[ [ 6, 12 ] ][128X[104X
    [4X[25Xgap>[125X [27Xirr:= Irr( tbl );;[127X[104X
    [4X[25Xgap>[125X [27XPIMs:= TransposedMat( DecompositionMatrix( modtbl ) ) * irr;;[127X[104X
    [4X[25Xgap>[125X [27XSolutionMat( PIMs, irr[6] * irr[12] );[127X[104X
    [4X[28X[ 0, 0, 0, 1, 1, 1, 0, 0, -2, 3 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YChecking  all  available  tables from the library takes several hours of CPU
  time  and  also  requires  a  lot of space; finally, it yields the following
  result.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xexamples:= [];;[127X[104X
    [4X[25Xgap>[125X [27Xfor name in AllCharacterTableNames( IsDuplicateTable, false ) do[127X[104X
    [4X[25X>[125X [27X     tbl:= CharacterTable( name );[127X[104X
    [4X[25X>[125X [27X     for p in PrimeDivisors( Size( tbl ) ) do[127X[104X
    [4X[25X>[125X [27X       modtbl:= tbl mod p;[127X[104X
    [4X[25X>[125X [27X       if modtbl <> fail then[127X[104X
    [4X[25X>[125X [27X         res:= GenProjNotProj( modtbl );[127X[104X
    [4X[25X>[125X [27X         if not IsEmpty( res ) then[127X[104X
    [4X[25X>[125X [27X           AddSet( examples, [ name, p, Length( res ) ] );[127X[104X
    [4X[25X>[125X [27X        fi;[127X[104X
    [4X[25X>[125X [27X      fi;[127X[104X
    [4X[25X>[125X [27X    od;[127X[104X
    [4X[25X>[125X [27X  od;[127X[104X
    [4X[25Xgap>[125X [27Xexamples;[127X[104X
    [4X[28X[ [ "(A5xJ2):2", 2, 4 ], [ "(D10xJ2).2", 2, 9 ], [ "2.Suz", 3, 1 ], [128X[104X
    [4X[28X  [ "2.Suz.2", 3, 4 ], [ "2xCo2", 5, 4 ], [ "3.Suz", 2, 6 ], [128X[104X
    [4X[28X  [ "3.Suz.2", 2, 4 ], [ "Co2", 5, 1 ], [ "Co3", 2, 4 ], [128X[104X
    [4X[28X  [ "Isoclinic(2.Suz.2)", 3, 4 ], [ "J2", 2, 1 ], [ "Suz", 2, 2 ], [128X[104X
    [4X[28X  [ "Suz", 3, 1 ], [ "Suz.2", 3, 4 ] ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThis  list  looks  rather [21Xsporadic[121X. The number of examples is small, and all
  groups  in question except two (the subdirect products of [22XS_5[122X and [22XJ_2.2[122X, and
  of [22X5:4[122X and [22XJ_2.2[122X, respectively) are extensions of sporadic simple groups.[133X
  
  [33X[0;0YNote  that  the  following  cases could be omitted because the characters in
  question belong to proper factor groups: [22X2.Suz[122X mod [22X3[122X, [22X2.Suz.2[122X mod [22X3[122X, and its
  isoclinic variant.[133X
  
  
  [1X2.3-10  [33X[0;0YExample:  Certain elementary abelian subgroups in quasisimple groups[101X
  [1X(November 2020)[133X[101X
  
  [33X[0;0YIn  October 2020, Bob Guralnick asked: Does each quasisimple group [22XG[122X contain
  an  elementary  abelian  subgroup  that contains elements from all conjugacy
  classes  of involutions in [22XG[122X? (Such a subgroup is called a [13Xbroad[113X subgroup of
  [22XG[122X. See [GR] for the paper.)[133X
  
  [33X[0;0YIn the case of simple groups, theoretical arguments suffice to show that the
  answer  is  positive  for simple groups of alternating and Lie type, thus it
  remains to inspect the sporadic simple groups.[133X
  
  [33X[0;0YIn  the case of nonsimple quasisimple groups, again groups having a sporadic
  simple  factor  group have to be checked, and also the central extensions of
  groups   of   Lie  type  by  exceptional  multipliers  have  to  be  checked
  computationally.[133X
  
  [33X[0;0YIn the following situations, the answer is positive for a given group [22XG[122X.[133X
  
  [31X1[131X   [33X[0;6Y[22XG[122X has at most two classes of involutions. (Take an involution [22Xx[122X in the
        centre  of a Sylow [22X2[122X-subgroup [22XP[122X of [22XG[122X; if there is a conjugacy class of
        involutions  in [22XG[122X different from [22Xx^G[122X then [22XP[122X contains an element in the
        other involution class.)[133X
  
  [31X2[131X   [33X[0;6Y[22XG[122X  has  exactly  three  classes  of  involutions  such  that there are
        representatives  [22Xx[122X, [22Xy[122X, [22Xz[122X with the property [22Xx y = z[122X. (The subgroup [22X⟨ x,
        y  ⟩[122X  is  a Klein four group; note that [22Xx[122X and [22Xy[122X commute because [22Xx^{-1}
        y^{-1} x y = (x y)^2 = z^2 = 1[122X holds.)[133X
  
  [31X3[131X   [33X[0;6Y[22XG[122X  has  a  central  elementary  abelian  [22X2[122X-subgroup [22XN[122X, and there is an
        elementary  abelian [22X2[122X-subgroup [22XP / N[122X in [22XG / N[122X containing elements from
        all  those  involution classes of [22XG / N[122X that lift to involutions of [22XG[122X,
        but no elements from other involution classes of [22XG / N[122X. (Just take the
        preimage [22XP[122X, which is elementary abelian.)[133X
  
        [33X[0;6YThis  condition is satisfied for example if the answer is positive for
        [22XG  /  N[122X  and  [13Xall[113X involutions of [22XG / N[122X lift to involutions in [22XG[122X, or if
        exactly one class of involutions of [22XG / N[122X lifts to involutions in [22XG[122X.[133X
  
  [33X[0;0YThe  following  function  evaluates  the first two of the above criteria and
  easy cases of the third one, for the given character table of the group [22XG[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XApplyCriteria:= "dummy";;  # Avoid a syntax error ...[127X[104X
    [4X[25Xgap>[125X [27XApplyCriteria:= function( tbl )[127X[104X
    [4X[25X>[125X [27X   local id, ord, invpos, cen, facttbl, factfus, invmap, factord,[127X[104X
    [4X[25X>[125X [27X          factinvpos, imgs;[127X[104X
    [4X[25X>[125X [27X   id:= ReplacedString( Identifier( tbl ), " ", "" );[127X[104X
    [4X[25X>[125X [27X   ord:= OrdersClassRepresentatives( tbl );[127X[104X
    [4X[25X>[125X [27X   invpos:= PositionsProperty( ord, x -> x <= 2 );[127X[104X
    [4X[25X>[125X [27X   if Length( invpos ) <= 3 then[127X[104X
    [4X[25X>[125X [27X     # There are at most 2 involution classes.[127X[104X
    [4X[25X>[125X [27X     Print( "#I  ", id, ": ",[127X[104X
    [4X[25X>[125X [27X            "done (", Length( invpos ) - 1, " inv. class(es))\n" );[127X[104X
    [4X[25X>[125X [27X     return true;[127X[104X
    [4X[25X>[125X [27X   elif Length( invpos ) = 4 and[127X[104X
    [4X[25X>[125X [27X        ClassMultiplicationCoefficient( tbl, invpos[2], invpos[3],[127X[104X
    [4X[25X>[125X [27X                                             invpos[4] ) <> 0 then[127X[104X
    [4X[25X>[125X [27X     Print( "#I  ", id, ": ",[127X[104X
    [4X[25X>[125X [27X            "done (3 inv. classes, nonzero str. const.)\n" );[127X[104X
    [4X[25X>[125X [27X     return true;[127X[104X
    [4X[25X>[125X [27X   fi;[127X[104X
    [4X[25X>[125X [27X   cen:= Intersection( invpos, ClassPositionsOfCentre( tbl ) );[127X[104X
    [4X[25X>[125X [27X   if Length( cen ) > 1 then[127X[104X
    [4X[25X>[125X [27X     # Consider the factor modulo the largest central el. ab. 2-group.[127X[104X
    [4X[25X>[125X [27X     facttbl:= tbl / cen;[127X[104X
    [4X[25X>[125X [27X     factfus:= GetFusionMap( tbl, facttbl );[127X[104X
    [4X[25X>[125X [27X     invmap:= InverseMap( factfus );[127X[104X
    [4X[25X>[125X [27X     factord:= OrdersClassRepresentatives( facttbl );[127X[104X
    [4X[25X>[125X [27X     factinvpos:= PositionsProperty( factord, x -> x <= 2 );[127X[104X
    [4X[25X>[125X [27X     if ForAll( factinvpos,[127X[104X
    [4X[25X>[125X [27X            i -> invmap[i] in invpos or[127X[104X
    [4X[25X>[125X [27X                 ( IsList( invmap[i] ) and[127X[104X
    [4X[25X>[125X [27X                   IsSubset( invpos, invmap[i] ) ) ) then[127X[104X
    [4X[25X>[125X [27X       # All involutions of the factor group lift to involutions.[127X[104X
    [4X[25X>[125X [27X       if ApplyCriteria( facttbl ) = true then[127X[104X
    [4X[25X>[125X [27X         Print( "#I  ", id, ": ",[127X[104X
    [4X[25X>[125X [27X                "done (all inv. in ",[127X[104X
    [4X[25X>[125X [27X                ReplacedString( Identifier( facttbl ), " ", "" ),[127X[104X
    [4X[25X>[125X [27X                " lift to inv.)\n" );[127X[104X
    [4X[25X>[125X [27X         return true;[127X[104X
    [4X[25X>[125X [27X       fi;[127X[104X
    [4X[25X>[125X [27X     fi;[127X[104X
    [4X[25X>[125X [27X     imgs:= Set( factfus{ invpos } );[127X[104X
    [4X[25X>[125X [27X     if Length( imgs ) = 2 and[127X[104X
    [4X[25X>[125X [27X        ForAll( imgs,[127X[104X
    [4X[25X>[125X [27X            i -> invmap[i] in invpos or[127X[104X
    [4X[25X>[125X [27X                 ( IsList( invmap[i] ) and[127X[104X
    [4X[25X>[125X [27X                   IsSubset( invpos, invmap[i] ) ) ) then[127X[104X
    [4X[25X>[125X [27X       # There is a C2 subgroup of the factor[127X[104X
    [4X[25X>[125X [27X       # such that its involution lifts to involutions,[127X[104X
    [4X[25X>[125X [27X       # and the lifts of the C2 cover all involution classes of 'tbl'.[127X[104X
    [4X[25X>[125X [27X       Print( "#I  ", id, ": ",[127X[104X
    [4X[25X>[125X [27X              "done (all inv. in ", id,[127X[104X
    [4X[25X>[125X [27X              " are lifts of a C2\n",[127X[104X
    [4X[25X>[125X [27X              "#I  in the factor modulo ",[127X[104X
    [4X[25X>[125X [27X              ReplacedString( String( cen ), " ", "" ), ")\n" );[127X[104X
    [4X[25X>[125X [27X       return true;[127X[104X
    [4X[25X>[125X [27X     fi;[127X[104X
    [4X[25X>[125X [27X   fi;[127X[104X
    [4X[25X>[125X [27X   Print( "#I  ", id, ": ",[127X[104X
    [4X[25X>[125X [27X          "OPEN (", Length( invpos  ) - 1, " inv. class(es))\n" );[127X[104X
    [4X[25X>[125X [27X   return false;[127X[104X
    [4X[25X>[125X [27Xend;;[127X[104X
  [4X[32X[104X
  
  [33X[0;0YWe start with the sporadic simple groups.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XSizeScreen( [ 72 ] );;[127X[104X
    [4X[25Xgap>[125X [27Xspor:= AllCharacterTableNames( IsSporadicSimple, true,[127X[104X
    [4X[25X>[125X [27X                                  IsDuplicateTable, false );[127X[104X
    [4X[28X[ "B", "Co1", "Co2", "Co3", "F3+", "Fi22", "Fi23", "HN", "HS", "He", [128X[104X
    [4X[28X  "J1", "J2", "J3", "J4", "Ly", "M", "M11", "M12", "M22", "M23", [128X[104X
    [4X[28X  "M24", "McL", "ON", "Ru", "Suz", "Th" ][128X[104X
    [4X[25Xgap>[125X [27XFiltered( spor,[127X[104X
    [4X[25X>[125X [27X       x -> not ApplyCriteria( CharacterTable( x ) ) );[127X[104X
    [4X[28X#I  B: OPEN (4 inv. class(es))[128X[104X
    [4X[28X#I  Co1: OPEN (3 inv. class(es))[128X[104X
    [4X[28X#I  Co2: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  Co3: done (2 inv. class(es))[128X[104X
    [4X[28X#I  F3+: done (2 inv. class(es))[128X[104X
    [4X[28X#I  Fi22: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  Fi23: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  HN: done (2 inv. class(es))[128X[104X
    [4X[28X#I  HS: done (2 inv. class(es))[128X[104X
    [4X[28X#I  He: done (2 inv. class(es))[128X[104X
    [4X[28X#I  J1: done (1 inv. class(es))[128X[104X
    [4X[28X#I  J2: done (2 inv. class(es))[128X[104X
    [4X[28X#I  J3: done (1 inv. class(es))[128X[104X
    [4X[28X#I  J4: done (2 inv. class(es))[128X[104X
    [4X[28X#I  Ly: done (1 inv. class(es))[128X[104X
    [4X[28X#I  M: done (2 inv. class(es))[128X[104X
    [4X[28X#I  M11: done (1 inv. class(es))[128X[104X
    [4X[28X#I  M12: done (2 inv. class(es))[128X[104X
    [4X[28X#I  M22: done (1 inv. class(es))[128X[104X
    [4X[28X#I  M23: done (1 inv. class(es))[128X[104X
    [4X[28X#I  M24: done (2 inv. class(es))[128X[104X
    [4X[28X#I  McL: done (1 inv. class(es))[128X[104X
    [4X[28X#I  ON: done (1 inv. class(es))[128X[104X
    [4X[28X#I  Ru: done (2 inv. class(es))[128X[104X
    [4X[28X#I  Suz: done (2 inv. class(es))[128X[104X
    [4X[28X#I  Th: done (1 inv. class(es))[128X[104X
    [4X[28X[ "B", "Co1" ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe two open cases can be handled as follows.[133X
  
  [33X[0;0YThe  group  [22XG  =  B[122X  contains  maximal subgroups of the type [22X5:4 × HS.2[122X (the
  normalizers  of  [10X5A[110X  elements,  see [CCN+85, p. 217]). The direct factor [22XH =
  HS.2[122X  of  such a subgroup has four classes of involutions, which fuse to the
  four involution classes of [22XG[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "B" );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpos:= Positions( OrdersClassRepresentatives( t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5 ][128X[104X
    [4X[25Xgap>[125X [27Xmx:= List( Maxes( t ), CharacterTable );;[127X[104X
    [4X[25Xgap>[125X [27Xs:= First( mx,[127X[104X
    [4X[25X>[125X [27X         x -> Size( x ) = 20 * Size( CharacterTable( "HS.2" ) ) );[127X[104X
    [4X[28XCharacterTable( "5:4xHS.2" )[128X[104X
    [4X[25Xgap>[125X [27Xfus:= GetFusionMap( s, t );;[127X[104X
    [4X[25Xgap>[125X [27Xprod:= ClassPositionsOfDirectProductDecompositions( s );[127X[104X
    [4X[28X[ [ [ 1, 40 .. 157 ], [ 1 .. 39 ] ] ][128X[104X
    [4X[25Xgap>[125X [27XfusinB:= List( prod[1], l -> fus{ l } );[127X[104X
    [4X[28X[ [ 1, 18, 8, 3, 8 ], [128X[104X
    [4X[28X  [ 1, 3, 4, 6, 8, 9, 14, 19, 18, 18, 25, 22, 31, 36, 43, 51, 50, 54, [128X[104X
    [4X[28X      57, 81, 100, 2, 5, 8, 11, 16, 21, 20, 24, 34, 33, 48, 52, 59, [128X[104X
    [4X[28X      76, 106, 100, 100, 137 ] ][128X[104X
    [4X[25Xgap>[125X [27XIsSubset( fusinB[2], invpos );[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xh:= CharacterTable( "HS.2" );;[127X[104X
    [4X[25Xgap>[125X [27XfusinB[2]{ Positions( OrdersClassRepresentatives( h ), 2 ) };[127X[104X
    [4X[28X[ 3, 4, 2, 5 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe table of marks of [22XH[122X is known. We find five classes of elementary abelian
  subgroups of order eight in [22XH[122X that contain elements from all four involution
  classes of [22XH[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xtom:= TableOfMarks( h );[127X[104X
    [4X[28XTableOfMarks( "HS.2" )[128X[104X
    [4X[25Xgap>[125X [27Xord:= OrdersTom( tom );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpos:= Positions( ord, 2 );[127X[104X
    [4X[28X[ 2, 3, 534, 535 ][128X[104X
    [4X[25Xgap>[125X [27X8pos:= Positions( ord, 8 );;[127X[104X
    [4X[25Xgap>[125X [27Xfilt:= Filtered( 8pos,[127X[104X
    [4X[25X>[125X [27X       x -> ForAll( invpos,[127X[104X
    [4X[25X>[125X [27X              y -> Length( IntersectionsTom( tom, x, y ) ) >= y[127X[104X
    [4X[25X>[125X [27X                   and IntersectionsTom( tom, x, y )[y] <> 0 ) );[127X[104X
    [4X[28X[ 587, 589, 590, 593, 595 ][128X[104X
    [4X[25Xgap>[125X [27Xreps:= List( filt, i -> RepresentativeTom( tom, i ) );;[127X[104X
    [4X[25Xgap>[125X [27XForAll( reps, IsElementaryAbelian );[127X[104X
    [4X[28Xtrue[128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe  group [22XG = Co_1[122X has a maximal subgroup [22XH[122X of type [22XA_9 × S_3[122X (see [CCN+85,
  p. 183])  that  contains  elements  from  all three involution classes of [22XG[122X.
  Moreover,  the  factor [22XS_3[122X contains [10X2A[110X elements, and the factor [22XA_9[122X contains
  [10X2B[110X  and  [10X2C[110X elements. This yields the desired elementary abelian subgroup of
  order eight.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "Co1" );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpos:= Positions( OrdersClassRepresentatives( t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4 ][128X[104X
    [4X[25Xgap>[125X [27Xmx:= List( Maxes( t ), CharacterTable );;[127X[104X
    [4X[25Xgap>[125X [27Xs:= First( mx, x -> Size( x ) = 3 * Factorial( 9 ) );[127X[104X
    [4X[28XCharacterTable( "A9xS3" )[128X[104X
    [4X[25Xgap>[125X [27Xfus:= GetFusionMap( s, t );;[127X[104X
    [4X[25Xgap>[125X [27Xprod:= ClassPositionsOfDirectProductDecompositions( s );[127X[104X
    [4X[28X[ [ [ 1 .. 3 ], [ 1, 4 .. 52 ] ] ][128X[104X
    [4X[25Xgap>[125X [27XList( prod[1], l -> fus{ l } );[127X[104X
    [4X[28X[ [ 1, 8, 2 ], [128X[104X
    [4X[28X  [ 1, 3, 4, 5, 7, 6, 13, 14, 15, 19, 24, 28, 36, 37, 39, 50, 61, 61 [128X[104X
    [4X[28X     ] ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThus  we  know  that  the answer is positive for each sporadic simple group.
  Next  we look at the relevant covering groups of sporadic simple groups. For
  a  quasisimple group with a sporadic simple factor, the Schur multiplier has
  at  most  the prime factors [22X2[122X and [22X3[122X; only the extension by the [22X2[122X-part of the
  multipier must be checked.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xsporcov:= AllCharacterTableNames( IsSporadicSimple, true,[127X[104X
    [4X[25X>[125X [27X       IsDuplicateTable, false, OfThose, SchurCover );[127X[104X
    [4X[28X[ "12.M22", "2.B", "2.Co1", "2.HS", "2.J2", "2.M12", "2.Ru", "3.F3+", [128X[104X
    [4X[28X  "3.J3", "3.McL", "3.ON", "6.Fi22", "6.Suz", "Co2", "Co3", "Fi23", [128X[104X
    [4X[28X  "HN", "He", "J1", "J4", "Ly", "M", "M11", "M23", "M24", "Th" ][128X[104X
    [4X[25Xgap>[125X [27XFiltered( sporcov, x -> '.' in x );[127X[104X
    [4X[28X[ "12.M22", "2.B", "2.Co1", "2.HS", "2.J2", "2.M12", "2.Ru", "3.F3+", [128X[104X
    [4X[28X  "3.J3", "3.McL", "3.ON", "6.Fi22", "6.Suz" ][128X[104X
    [4X[25Xgap>[125X [27Xrelevant:= [ "2.M22", "4.M22", "2.B", "2.Co1", "2.HS", "2.J2",[127X[104X
    [4X[25X>[125X [27X                "2.M12", "2.Ru", "2.Fi22", "2.Suz" ];;[127X[104X
    [4X[25Xgap>[125X [27XFiltered( relevant,[127X[104X
    [4X[25X>[125X [27X       x -> not ApplyCriteria( CharacterTable( x ) ) );[127X[104X
    [4X[28X#I  2.M22: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  4.M22: done (2 inv. class(es))[128X[104X
    [4X[28X#I  2.B: OPEN (5 inv. class(es))[128X[104X
    [4X[28X#I  2.Co1: OPEN (4 inv. class(es))[128X[104X
    [4X[28X#I  2.HS: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2.J2: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2.M12: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2.Ru: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2.Fi22/[1,2]: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2.Fi22: done (all inv. in 2.Fi22/[1,2] lift to inv.)[128X[104X
    [4X[28X#I  2.Suz: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X[ "2.B", "2.Co1" ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe  group  [22XB[122X  has four classes of involutions, let us call them [10X2A[110X, [10X2B[110X, [10X2C[110X,
  and [10X2D[110X. All except [10X2C[110X lift to involutions in [22X2.B[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "B" );;[127X[104X
    [4X[25Xgap>[125X [27X2t:= CharacterTable( "2.B" );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpost:= Positions( OrdersClassRepresentatives( t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5 ][128X[104X
    [4X[25Xgap>[125X [27Xinvpos2t:= Positions( OrdersClassRepresentatives( 2t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5, 7 ][128X[104X
    [4X[25Xgap>[125X [27XGetFusionMap( 2t, t ){ invpos2t };[127X[104X
    [4X[28X[ 1, 2, 3, 3, 5 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThus  it  suffices  to  show  that there is a subgroup of type [22X2^2[122X in [22XB[122X that
  contains elements from [10X2A[110X, [10X2B[110X, and [10X2D[110X (but no element from [10X2C[110X). This follows
  from the fact that the [22X([122X[10X2A[110X, [10X2B[110X, [10X2D[110X[22X)[122X structure constant of [22XB[122X is nonzero.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XClassMultiplicationCoefficient( t, 2, 3, 5 );[127X[104X
    [4X[28X120[128X[104X
  [4X[32X[104X
  
  [33X[0;0YThe  group  [22XCo_1[122X  has three classes of involutions, let us call them [10X2A[110X, [10X2B[110X,
  and [10X2C[110X. All except [10X2B[110X lift to involutions in [22X2.Co_1[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "Co1" );;[127X[104X
    [4X[25Xgap>[125X [27X2t:= CharacterTable( "2.Co1" );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpost:= Positions( OrdersClassRepresentatives( t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4 ][128X[104X
    [4X[25Xgap>[125X [27Xinvpos2t:= Positions( OrdersClassRepresentatives( 2t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 6 ][128X[104X
    [4X[25Xgap>[125X [27XGetFusionMap( 2t, t ){ invpos2t };[127X[104X
    [4X[28X[ 1, 2, 2, 4 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThus  it  suffices to show that there is a subgroup of type [22X2^2[122X in [22XCo_1[122X that
  contains  elements  from [10X2A[110X and [10X2C[110X but no element from [10X2B[110X. This follows from
  the fact that the [22X([122X[10X2A[110X, [10X2A[110X, [10X2C[110X[22X)[122X structure constant of [22XCo_1[122X is nonzero.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XClassMultiplicationCoefficient( t, 2, 2, 4 );[127X[104X
    [4X[28X264[128X[104X
  [4X[32X[104X
  
  [33X[0;0YFinally,  we  deal  with  the  relevant  central extensions of finite simple
  groups  of Lie type with exceptional multipliers. These groups are listed in
  [CCN+85,  p. xvi,  Table  5].  The  following  cases  belong  to exceptional
  multipliers with nontrivial [22X2[122X-part.[133X
  
      ┌─────────────────┬──────────┬────────────┐
      │ Group           │ Name     │ Multiplier │ 
      ├─────────────────┼──────────┼────────────┤
      │ [22XA_1(4)[122X          │ [10X"A5"[110X     │          [22X2[122X │ 
      │ [22XA_2(2)[122X          │ [10X"L3(2)"[110X  │          [22X2[122X │ 
      │ [22XA_2(4)[122X          │ [10X"L3(4)"[110X  │        [22X4^2[122X │ 
      │ [22XA_3(2)[122X          │ [10X"A8"[110X     │          [22X2[122X │ 
      │ [22X^2A_3(2)[122X        │ [10X"U4(2)"[110X  │          [22X2[122X │ 
      │ [22X^2A_5(2)[122X        │ [10X"U6(2)"[110X  │        [22X2^2[122X │ 
      │ [22XB_2(2)[122X          │ [10X"S6"[110X     │          [22X2[122X │ 
      │ [22X^2B_2(2)[122X        │ [10X"Sz(8)"[110X  │        [22X2^2[122X │ 
      │ [22XB_3(2) ≅ C_3(2)[122X │ [10X"S6(2)"[110X  │          [22X2[122X │ 
      │ [22XD_4(2)[122X          │ [10X"O8+(2)"[110X │        [22X2^2[122X │ 
      │ [22XG_2(4)[122X          │ [10X"G2(4)"[110X  │          [22X2[122X │ 
      │ [22XF_4(2)[122X          │ [10X"F4(2)"[110X  │          [22X2[122X │ 
      │ [22X^2E_6(2)[122X        │ [10X"2E6(2)"[110X │        [22X2^2[122X │ 
      └─────────────────┴──────────┴────────────┘
  
       [1XTable:[101X Groups with exceptional [22X2[122X-part of their multiplier
  
  
  [33X[0;0YThis  leads to the following list of cases to be checked. (We would not need
  to  deal with the groups [22XA_5[122X and [22XL_3(2)[122X, because of isomorphisms with groups
  of  Lie  type  for  which the multiplier in question is not exceptional, but
  here we ignore this fact.)[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xlist:= [[127X[104X
    [4X[25X>[125X [27X     [ "A5", "2.A5" ],[127X[104X
    [4X[25X>[125X [27X     [ "L3(2)", "2.L3(2)" ],[127X[104X
    [4X[25X>[125X [27X     [ "L3(4)", "2.L3(4)", "2^2.L3(4)", "4_1.L3(4)", "4_2.L3(4)",[127X[104X
    [4X[25X>[125X [27X       "(2x4).L3(4)", "4^2.L3(4)" ],[127X[104X
    [4X[25X>[125X [27X     [ "A8", "2.A8" ],[127X[104X
    [4X[25X>[125X [27X     [ "U4(2)", "2.U4(2)"],[127X[104X
    [4X[25X>[125X [27X     [ "U6(2)", "2.U6(2)", "2^2.U6(2)" ],[127X[104X
    [4X[25X>[125X [27X     [ "A6", "2.A6" ],[127X[104X
    [4X[25X>[125X [27X     [ "Sz(8)", "2.Sz(8)", "2^2.Sz(8)" ],[127X[104X
    [4X[25X>[125X [27X     [ "S6(2)", "2.S6(2)" ],[127X[104X
    [4X[25X>[125X [27X     [ "O8+(2)", "2.O8+(2)", "2^2.O8+(2)" ],[127X[104X
    [4X[25X>[125X [27X     [ "G2(4)", "2.G2(4)" ],[127X[104X
    [4X[25X>[125X [27X     [ "F4(2)", "2.F4(2)" ],[127X[104X
    [4X[25X>[125X [27X     [ "2E6(2)", "2.2E6(2)", "2^2.2E6(2)" ] ];;[127X[104X
    [4X[25Xgap>[125X [27XFiltered( Concatenation( list ),[127X[104X
    [4X[25X>[125X [27X       x -> not ApplyCriteria( CharacterTable( x ) ) );[127X[104X
    [4X[28X#I  A5: done (1 inv. class(es))[128X[104X
    [4X[28X#I  2.A5: done (1 inv. class(es))[128X[104X
    [4X[28X#I  L3(2): done (1 inv. class(es))[128X[104X
    [4X[28X#I  2.L3(2): done (1 inv. class(es))[128X[104X
    [4X[28X#I  L3(4): done (1 inv. class(es))[128X[104X
    [4X[28X#I  2.L3(4): done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2^2.L3(4)/[1,2,3,4]: done (1 inv. class(es))[128X[104X
    [4X[28X#I  2^2.L3(4): done (all inv. in 2^2.L3(4)/[1,2,3,4] lift to inv.)[128X[104X
    [4X[28X#I  4_1.L3(4): done (2 inv. class(es))[128X[104X
    [4X[28X#I  4_2.L3(4): done (2 inv. class(es))[128X[104X
    [4X[28X#I  (2x4).L3(4): done (all inv. in (2x4).L3(4) are lifts of a C2[128X[104X
    [4X[28X#I  in the factor modulo [1,2,3,4])[128X[104X
    [4X[28X#I  4^2.L3(4): done (all inv. in 4^2.L3(4) are lifts of a C2[128X[104X
    [4X[28X#I  in the factor modulo [1,2,3,4])[128X[104X
    [4X[28X#I  A8: done (2 inv. class(es))[128X[104X
    [4X[28X#I  2.A8: done (2 inv. class(es))[128X[104X
    [4X[28X#I  U4(2): done (2 inv. class(es))[128X[104X
    [4X[28X#I  2.U4(2): done (2 inv. class(es))[128X[104X
    [4X[28X#I  U6(2): done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2.U6(2)/[1,2]: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2.U6(2): done (all inv. in 2.U6(2)/[1,2] lift to inv.)[128X[104X
    [4X[28X#I  2^2.U6(2)/[1,2,3,4]: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2^2.U6(2): done (all inv. in 2^2.U6(2)/[1,2,3,4] lift to inv.)[128X[104X
    [4X[28X#I  A6: done (1 inv. class(es))[128X[104X
    [4X[28X#I  2.A6: done (1 inv. class(es))[128X[104X
    [4X[28X#I  Sz(8): done (1 inv. class(es))[128X[104X
    [4X[28X#I  2.Sz(8): done (2 inv. class(es))[128X[104X
    [4X[28X#I  2^2.Sz(8)/[1,2,3,4]: done (1 inv. class(es))[128X[104X
    [4X[28X#I  2^2.Sz(8): done (all inv. in 2^2.Sz(8)/[1,2,3,4] lift to inv.)[128X[104X
    [4X[28X#I  S6(2): OPEN (4 inv. class(es))[128X[104X
    [4X[28X#I  2.S6(2): OPEN (3 inv. class(es))[128X[104X
    [4X[28X#I  O8+(2): OPEN (5 inv. class(es))[128X[104X
    [4X[28X#I  2.O8+(2): OPEN (5 inv. class(es))[128X[104X
    [4X[28X#I  2^2.O8+(2): OPEN (5 inv. class(es))[128X[104X
    [4X[28X#I  G2(4): done (2 inv. class(es))[128X[104X
    [4X[28X#I  2.G2(4): done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  F4(2): OPEN (4 inv. class(es))[128X[104X
    [4X[28X#I  2.F4(2)/[1,2]: OPEN (4 inv. class(es))[128X[104X
    [4X[28X#I  2.F4(2): OPEN (9 inv. class(es))[128X[104X
    [4X[28X#I  2E6(2): done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2.2E6(2)/[1,2]: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2.2E6(2): done (all inv. in 2.2E6(2)/[1,2] lift to inv.)[128X[104X
    [4X[28X#I  2^2.2E6(2)/[1,2,3,4]: done (3 inv. classes, nonzero str. const.)[128X[104X
    [4X[28X#I  2^2.2E6(2): done (all inv. in 2^2.2E6(2)/[1,2,3,4] lift to inv.)[128X[104X
    [4X[28X[ "S6(2)", "2.S6(2)", "O8+(2)", "2.O8+(2)", "2^2.O8+(2)", "F4(2)", [128X[104X
    [4X[28X  "2.F4(2)" ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YWe  could  assume  that  the answer is positive for the simple groups in the
  list  of  open  cases, by theoretical arguments, but it is easy to show this
  computationally.[133X
  
  [33X[0;0YFor  [22XG  =  S_6(2)[122X, consider a maximal subgroup [22X2^6.L_3(2)[122X of [22XG[122X (see [CCN+85,
  p. 46]):  Its  [22X2[122X-core  is  elementary abelian and covers all four involution
  classes of [22XG[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "S6(2)" );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpos:= Positions( OrdersClassRepresentatives( t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5 ][128X[104X
    [4X[25Xgap>[125X [27Xmx:= List( Maxes( t ), CharacterTable );;[127X[104X
    [4X[25Xgap>[125X [27Xs:= First( mx,[127X[104X
    [4X[25X>[125X [27X         x -> Size( x ) = 2^6 * Size( CharacterTable( "L3(2)" ) ) );[127X[104X
    [4X[28XCharacterTable( "2^6:L3(2)" )[128X[104X
    [4X[25Xgap>[125X [27Xcorepos:= ClassPositionsOfPCore( s, 2 );[127X[104X
    [4X[28X[ 1 .. 5 ][128X[104X
    [4X[25Xgap>[125X [27XOrdersClassRepresentatives( t ){ corepos };[127X[104X
    [4X[28X[ 1, 2, 2, 2, 2 ][128X[104X
    [4X[25Xgap>[125X [27XGetFusionMap( s, t ){ corepos };[127X[104X
    [4X[28X[ 1, 3, 4, 2, 5 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YConcerning  [22XG  =  2.S_6(2)[122X,  note  that  from the four involution classes of
  [22XS_6(2)[122X, exactly [10X2B[110X and [10X2D[110X lift to involutions in [22X2.S_6(2)[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27X2t:= CharacterTable( "2.S6(2)" );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpost:= Positions( OrdersClassRepresentatives( t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5 ][128X[104X
    [4X[25Xgap>[125X [27Xinvpos2t:= Positions( OrdersClassRepresentatives( 2t ), 2 );[127X[104X
    [4X[28X[ 2, 4, 6 ][128X[104X
    [4X[25Xgap>[125X [27XGetFusionMap( 2t, t ){ invpos2t };[127X[104X
    [4X[28X[ 1, 3, 5 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThus it suffices to show that there is a subgroup of type [22X2^2[122X in [22XS_6(2)[122X that
  contains elements from [10X2B[110X and [10X2D[110X but no elements from [10X2A[110X or [10X2C[110X. This follows
  from the fact that the [22X([122X[10X2B[110X, [10X2D[110X, [10X2D[110X[22X)[122X structure constant of [22XS_6(2)[122X is nonzero.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XClassMultiplicationCoefficient( t, 3, 5, 5 );[127X[104X
    [4X[28X15[128X[104X
  [4X[32X[104X
  
  [33X[0;0YFor [22XG = O_8^+(2)[122X, we consider the known table of marks.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "O8+(2)" );;[127X[104X
    [4X[25Xgap>[125X [27Xtom:= TableOfMarks( t );[127X[104X
    [4X[28XTableOfMarks( "O8+(2)" )[128X[104X
    [4X[25Xgap>[125X [27Xord:= OrdersTom( tom );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpos:= Positions( ord, 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5, 6 ][128X[104X
    [4X[25Xgap>[125X [27X8pos:= Positions( ord, 8 );;[127X[104X
    [4X[25Xgap>[125X [27Xfilt:= Filtered( 8pos,[127X[104X
    [4X[25X>[125X [27X            x -> ForAll( invpos,[127X[104X
    [4X[25X>[125X [27X                   y -> Length( IntersectionsTom( tom, x, y ) ) >= y[127X[104X
    [4X[25X>[125X [27X                        and IntersectionsTom( tom, x, y )[y] <> 0 ) );[127X[104X
    [4X[28X[ 151, 153 ][128X[104X
    [4X[25Xgap>[125X [27Xreps:= List( filt, i -> RepresentativeTom( tom, i ) );;[127X[104X
    [4X[25Xgap>[125X [27XForAll( reps, IsElementaryAbelian );[127X[104X
    [4X[28Xtrue[128X[104X
  [4X[32X[104X
  
  [33X[0;0YConcerning  [22XG  =  2.O_8^+(2)[122X,  note that from the five involution classes of
  [22XO_8^+(2)[122X, exactly [10X2A[110X, [10X2B[110X, and [10X2E[110X lift to involutions in [22X2.O_8^+(2)[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27X2t:= CharacterTable( "2.O8+(2)" );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpost:= Positions( OrdersClassRepresentatives( t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5, 6 ][128X[104X
    [4X[25Xgap>[125X [27Xinvpos2t:= Positions( OrdersClassRepresentatives( 2t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5, 8 ][128X[104X
    [4X[25Xgap>[125X [27XGetFusionMap( 2t, t ){ invpos2t };[127X[104X
    [4X[28X[ 1, 2, 3, 3, 6 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThus  it  suffices  to  show  that  the  [22X([122X[10X2A[110X,  [10X2B[110X, [10X2E[110X[22X)[122X structure constant of
  [22XO_8^+(2)[122X is nonzero.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XClassMultiplicationCoefficient( t, 2, 3, 6 );[127X[104X
    [4X[28X4[128X[104X
  [4X[32X[104X
  
  [33X[0;0YConcerning  [22XG  = 2^2.O_8^+(2)[122X, note that from the five involution classes of
  [22XO_8^+(2)[122X,   exactly   the   first  and  the  last  lift  to  involutions  in
  [22X2^2.O_8^+(2)[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xv4t:= CharacterTable( "2^2.O8+(2)" );;[127X[104X
    [4X[25Xgap>[125X [27Xinvposv4t:= Positions( OrdersClassRepresentatives( v4t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5, 12 ][128X[104X
    [4X[25Xgap>[125X [27XGetFusionMap( v4t, t ){ invposv4t };[127X[104X
    [4X[28X[ 1, 1, 1, 2, 6 ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YThus it suffices to show that a corresponding structure constant of [22XO_8^+(2)[122X
  is nonzero.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XClassMultiplicationCoefficient( t, 2, 6, 6 );[127X[104X
    [4X[28X27[128X[104X
  [4X[32X[104X
  
  [33X[0;0YFor  [22XG  = F_4(2)[122X, consider a maximal subgroup [22X2^10.A_8[122X of a maximal subgroup
  [22XS_8(2)[122X of [22XG[122X (see [CCN+85, p. 123 and 170]): Its [22X2[122X-core is elementary abelian
  and covers all four involution classes of [22XG[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xt:= CharacterTable( "F4(2)" );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpost:= Positions( OrdersClassRepresentatives( t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5 ][128X[104X
    [4X[25Xgap>[125X [27X"S8(2)" in Maxes( t );[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xs:= CharacterTable( "S8(2)M4" );[127X[104X
    [4X[28XCharacterTable( "2^10.A8" )[128X[104X
    [4X[25Xgap>[125X [27Xcorepos:= ClassPositionsOfPCore( s, 2 );[127X[104X
    [4X[28X[ 1 .. 7 ][128X[104X
    [4X[25Xgap>[125X [27XOrdersClassRepresentatives( s ){ corepos };[127X[104X
    [4X[28X[ 1, 2, 2, 2, 2, 2, 2 ][128X[104X
    [4X[25Xgap>[125X [27Xposs:= PossibleClassFusions( s, t );;[127X[104X
    [4X[25Xgap>[125X [27XList( poss, map -> map{ corepos } );[127X[104X
    [4X[28X[ [ 1, 4, 2, 3, 4, 5, 5 ], [ 1, 4, 2, 3, 4, 5, 5 ], [128X[104X
    [4X[28X  [ 1, 4, 3, 2, 4, 5, 5 ], [ 1, 4, 3, 2, 4, 5, 5 ] ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YFinally, all involutions of [22XG[122X lift to involutions in [22X2.F_4(2)[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27X2t:= CharacterTable( "2.F4(2)" );;[127X[104X
    [4X[25Xgap>[125X [27Xinvpos2t:= Positions( OrdersClassRepresentatives( 2t ), 2 );[127X[104X
    [4X[28X[ 2, 3, 4, 5, 6, 7, 8, 9, 10 ][128X[104X
    [4X[25Xgap>[125X [27XGetFusionMap( 2t, t ){ invpos2t };[127X[104X
    [4X[28X[ 1, 2, 2, 3, 3, 4, 4, 5, 5 ][128X[104X
  [4X[32X[104X
  
