File: utils.gd

package info (click to toggle)
gap-atlasrep 2.1.9-1
  • links: PTS
  • area: main
  • in suites: forky, sid, trixie
  • size: 8,688 kB
  • sloc: xml: 20,993; javascript: 155; makefile: 113; sh: 1
file content (540 lines) | stat: -rw-r--r-- 22,854 bytes parent folder | download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
#############################################################################
##
#W  utils.gd             GAP 4 package AtlasRep                 Thomas Breuer
##
##  This file contains the declarations of utility functions for the
##  &ATLAS; of Group Representations.
##


#############################################################################
##
##  Class Names Used in the AtlasRep Package
##
##  <#GAPDoc Label="classnames">
##  <Subsection Label="subsect:Definition of ATLAS Class Names">
##  <Heading>Definition of &ATLAS; Class Names</Heading>
##
##  For the definition of class names of an almost simple group,
##  we assume that the ordinary character tables of all nontrivial normal
##  subgroups are shown in
##  the &ATLAS; of Finite Groups&nbsp;<Cite Key="CCN85"/>.
##  <P/>
##  Each class name is a string consisting of the element order of the class
##  in question followed by a combination of capital letters, digits, and
##  the characters <C>'</C> and <C>-</C> (starting with a capital letter).
##  For example, <C>1A</C>, <C>12A1</C>, and <C>3B'</C> denote
##  the class that contains the identity element,
##  a class of element order <M>12</M>,
##  and a class of element order <M>3</M>, respectively.
##  <P/>
##  <Enum>
##  <Item>
##      For the table of a <E>simple</E> group, the class names are the same
##      as returned by the two argument version of the &GAP; function
##      <Ref Func="ClassNames" BookName="ref"/>,
##      cf.&nbsp;<Cite Key="CCN85" Where="Chapter 7, Section 5"/>:
##      The classes are arranged w.&nbsp;r.&nbsp;t.&nbsp;increasing element
##      order and for each element order w.&nbsp;r.&nbsp;t.&nbsp;decreasing
##      centralizer order, the conjugacy classes that contain elements of
##      order <M>n</M> are named <M>n</M><C>A</C>, <M>n</M><C>B</C>,
##      <M>n</M><C>C</C>, <M>\ldots</M>;
##      the alphabet used here is potentially infinite, and reads
##      <C>A</C>, <C>B</C>, <C>C</C>, <M>\ldots</M>, <C>Z</C>, <C>A1</C>,
##      <C>B1</C>, <M>\ldots</M>, <C>A2</C>, <C>B2</C>, <M>\ldots</M>.
##      <P/>
##      For example, the classes of the alternating group <M>A_5</M> have the
##      names <C>1A</C>, <C>2A</C>, <C>3A</C>, <C>5A</C>, and <C>5B</C>.
##  </Item>
##  <Item>
##      Next we consider the case of an <E>upward extension</E> <M>G.A</M>
##      of a simple group <M>G</M> by a <E>cyclic</E> group of order
##      <M>A</M>.
##      The &ATLAS; defines class names for each element <M>g</M> of
##      <M>G.A</M> only w.&nbsp;r.&nbsp;t.&nbsp;the group <M>G.a</M>, say,
##      that is generated by <M>G</M> and <M>g</M>;
##      namely, there is a power of <M>g</M> (with the exponent coprime to
##      the order of <M>g</M>) for which the class has a name of the same
##      form as the class names for simple groups,
##      and the name of the class of <M>g</M>
##      w.&nbsp;r.&nbsp;t.&nbsp;<M>G.a</M> is then
##      obtained from this name by appending a suitable number of
##      dashes&nbsp;<C>'</C>.
##      So dashed class names refer exactly to those classes that are not
##      printed in the &ATLAS;.
##      <P/>
##      For example, those classes of the symmetric group <M>S_5</M> that do
##      not lie in <M>A_5</M> have the names <C>2B</C>, <C>4A</C>,
##      and <C>6A</C>.
##      The outer classes of the group <M>L_2(8).3</M> have the names
##      <C>3B</C>, <C>6A</C>, <C>9D</C>, and <C>3B'</C>, <C>6A'</C>,
##      <C>9D'</C>.
##      The outer elements of order <M>5</M> in the group <M>Sz(32).5</M>
##      lie in the classes with names <C>5B</C>, <C>5B'</C>, <C>5B''</C>,
##      and <C>5B'''</C>.
##      <P/>
##      In the group <M>G.A</M>, the class of <M>g</M> may fuse with other
##      classes.
##      The name of the class of <M>g</M> in <M>G.A</M> is obtained from the
##      names of the involved classes of <M>G.a</M> by concatenating their
##      names after removing the element order part from all of them except
##      the first one.
##      <P/>
##      For example, the elements of order <M>9</M> in the group
##      <M>L_2(27).6</M> are contained in the subgroup <M>L_2(27).3</M>
##      but not in <M>L_2(27)</M>.
##      In <M>L_2(27).3</M>, they lie in the classes <C>9A</C>, <C>9A'</C>,
##      <C>9B</C>, and <C>9B'</C>;
##      in <M>L_2(27).6</M>, these classes fuse to <C>9AB</C> and
##      <C>9A'B'</C>.
##  </Item>
##  <Item>
##      Now we define class names for <E>general upward extensions</E>
##      <M>G.A</M> of a simple group <M>G</M>.
##      Each element <M>g</M> of such a group lies in an upward extension
##      <M>G.a</M> by a cyclic group, and the class names
##      w.&nbsp;r.&nbsp;t.&nbsp;<M>G.a</M> are already defined.
##      The name of the class of <M>g</M> in <M>G.A</M> is obtained by
##      concatenating the names of the classes in the orbit of <M>G.A</M> on
##      the classes of cyclic upward extensions of <M>G</M>,
##      after ordering the names lexicographically and removing the element
##      order part from all of them except the first one.
##      An <E>exception</E> is the situation where dashed and non-dashed
##      class names appear in an orbit;
##      in this case, the dashed names are omitted.
##      <P/>
##      For example, the classes <C>21A</C> and <C>21B</C> of the group
##      <M>U_3(5).3</M> fuse in <M>U_3(5).S_3</M> to the class <C>21AB</C>,
##      and the class <C>2B</C> of <M>U_3(5).2</M> fuses with the involution
##      classes <C>2B'</C>, <C>2B''</C> in the groups
##      <M>U_3(5).2^{\prime}</M> and <M>U_3(5).2^{{\prime\prime}}</M>
##      to the class <C>2B</C> of <M>U_3(5).S_3</M>.
##      <P/>
##      It may happen that some names in the <C>outputs</C> component of a
##      record returned by <Ref Func="AtlasProgram"/>
##      do not uniquely determine the classes of the corresponding elements.
##      For example, the (algebraically conjugate) classes <C>39A</C> and
##      <C>39B</C> of the group <M>Co_1</M> have not been distinguished yet.
##      In such cases, the names used contain a minus sign <C>-</C>,
##      and mean <Q>one of the classes in the range described by the name
##      before and the name after the minus sign</Q>;
##      the element order part of the name does not appear after the minus
##      sign.
##      So the name <C>39A-B</C> for the group <M>Co_1</M> means
##      <C>39A</C> or <C>39B</C>,
##      and the name <C>20A-B'''</C> for the group <M>Sz(32).5</M> means
##      one of the classes of element order <M>20</M> in this group
##      (these classes lie outside the simple group <M>Sz</M>).
##  </Item>
##  <Item>
##      For a <E>downward extension</E> <M>m.G.A</M> of an almost simple
##      group <M>G.A</M> by a cyclic group of order <M>m</M>,
##      let <M>\pi</M> denote the natural epimorphism from <M>m.G.A</M>
##      onto <M>G.A</M>.
##      Each class name of <M>m.G.A</M> has the form <C>nX_0</C>,
##      <C>nX_1</C> etc.,
##      where <C>nX</C> is the class name of the image under <M>\pi</M>,
##      and the indices <C>0</C>, <C>1</C> etc. are chosen according to the
##      position of the class in the lifting order rows for <M>G</M>,
##      see&nbsp;<Cite Key="CCN85" Where="Chapter 7, Section 7,
##      and the example in Section 8"/>).
##      <P/>
##      For example, if <M>m = 6</M> then <C>1A_1</C> and <C>1A_5</C> denote
##      the classes containing the generators of the kernel of <M>\pi</M>,
##      that is, central elements of order <M>6</M>.
##  </Item>
##  </Enum>
##
##  </Subsection>
##  <#/GAPDoc>
##
#T  missing:
#T  general central downward extensions (<M>2^2</M>, <M>2 \times 4</M>, ...)
##


#############################################################################
##
#F  AtlasClassNames( <tbl> )
##
##  <#GAPDoc Label="AtlasClassNames">
##  <ManSection>
##  <Func Name="AtlasClassNames" Arg='tbl'/>
##
##  <Returns>
##  a list of class names.
##  </Returns>
##  <Description>
##  Let <A>tbl</A> be the ordinary or modular character table of a group
##  <M>G</M>, say, that is almost simple or a downward extension of an
##  almost simple group and such that <A>tbl</A> is an &ATLAS; table
##  from the &GAP; Character Table Library,
##  according to its <Ref Func="InfoText" BookName="ref"/> value.
##  Then <Ref Func="AtlasClassNames"/> returns the list of class names for
##  <M>G</M>, as defined
##  in Section&nbsp;<Ref Subsect="subsect:Definition of ATLAS Class Names"/>.
##  The ordering of class names is the same as the ordering of the columns
##  of <A>tbl</A>.
##  <P/>
##  (The function may work also for character tables that are not
##  &ATLAS; tables,
##  but then clearly the class names returned are somewhat arbitrary.)
##  <P/>
##  <Example><![CDATA[
##  gap> AtlasClassNames( CharacterTable( "L3(4).3" ) );
##  [ "1A", "2A", "3A", "4ABC", "5A", "5B", "7A", "7B", "3B", "3B'", 
##    "3C", "3C'", "6B", "6B'", "15A", "15A'", "15B", "15B'", "21A", 
##    "21A'", "21B", "21B'" ]
##  gap> AtlasClassNames( CharacterTable( "U3(5).2" ) );
##  [ "1A", "2A", "3A", "4A", "5A", "5B", "5CD", "6A", "7AB", "8AB", 
##    "10A", "2B", "4B", "6D", "8C", "10B", "12B", "20A", "20B" ]
##  gap> AtlasClassNames( CharacterTable( "L2(27).6" ) );
##  [ "1A", "2A", "3AB", "7ABC", "13ABC", "13DEF", "14ABC", "2B", "4A", 
##    "26ABC", "26DEF", "28ABC", "28DEF", "3C", "3C'", "6A", "6A'", 
##    "9AB", "9A'B'", "6B", "6B'", "12A", "12A'" ]
##  gap> AtlasClassNames( CharacterTable( "L3(4).3.2_2" ) );
##  [ "1A", "2A", "3A", "4ABC", "5AB", "7A", "7B", "3B", "3C", "6B", 
##    "15A", "15B", "21A", "21B", "2C", "4E", "6E", "8D", "14A", "14B" ]
##  gap> AtlasClassNames( CharacterTable( "3.A6" ) );
##  [ "1A_0", "1A_1", "1A_2", "2A_0", "2A_1", "2A_2", "3A_0", "3B_0", 
##    "4A_0", "4A_1", "4A_2", "5A_0", "5A_1", "5A_2", "5B_0", "5B_1", 
##    "5B_2" ]
##  gap> AtlasClassNames( CharacterTable( "2.A5.2" ) );
##  [ "1A_0", "1A_1", "2A_0", "3A_0", "3A_1", "5AB_0", "5AB_1", "2B_0", 
##    "4A_0", "4A_1", "6A_0", "6A_1" ]
##  ]]></Example>
##  </Description>
##  </ManSection>
##  <#/GAPDoc>
##
DeclareGlobalFunction( "AtlasClassNames" );


#############################################################################
##
#V  AtlasClassNamesOffsetInfo
##
##  <ManSection>
##  <Var Name="AtlasClassNamesOffsetInfo"/>
##
##  <Description>
##  This global variable describes the cyclic upwards extensions of those
##  simple groups whose ordinary character tables are contained in the
##  &ATLAS; of Finite Groups and for which the outer automorphism groups
##  are noncyclic.
##  </Description>
##  </ManSection>
##
DeclareGlobalVariable( "AtlasClassNamesOffsetInfo" );


#############################################################################
##
#F  AtlasCharacterNames( <tbl> )
##
##  <#GAPDoc Label="AtlasCharacterNames">
##  <ManSection>
##  <Func Name="AtlasCharacterNames" Arg='tbl'/>
##
##  <Returns>
##  a list of character names.
##  </Returns>
##  <Description>
##  Let <A>tbl</A> be the ordinary or modular character table of a simple
##  group.
##  <Ref Func="AtlasCharacterNames"/> returns a list of strings,
##  the <M>i</M>-th entry being the name of the <M>i</M>-th irreducible
##  character of <A>tbl</A>;
##  this name consists of the degree of this character followed by
##  distinguishing lowercase letters.
##  <P/>
##  <Example><![CDATA[
##  gap> AtlasCharacterNames( CharacterTable( "A5" ) );                   
##  [ "1a", "3a", "3b", "4a", "5a" ]
##  ]]></Example>
##  </Description>
##  </ManSection>
##  <#/GAPDoc>
##
DeclareGlobalFunction( "AtlasCharacterNames" );


#############################################################################
##
#F  StringOfAtlasProgramCycToCcls( <prgstring>, <tbl>, <mode> )
##
##  <ManSection>
##  <Func Name="StringOfAtlasProgramCycToCcls" Arg='prgstring, tbl, mode'/>
##
##  <Description>
##  The purpose of this utility program is to construct a straight line
##  program for computing conjugacy class representatives of a group <M>G</M>
##  from a straight line program for computing representatives of classes
##  of maximally cyclic subgroups of <M>G</M>;
##  the latter program is assumed to be given by the string <A>prgstring</A>.
##  The second argument <A>tbl</A> must be the ordinary character table of
##  <M>G</M>.
##  The third argument <A>mode</A> must be one of the strings <C>"names"</C>
##  or <C>"numbers"</C>; in the former case, the labels used are class names,
##  in the latter case they are numbers.
##  (Note that the labels used for the inputs are the outputs of the program
##  given by <A>prgstring</A>, which may be names even if <C>"numbers"</C> is
##  chosen for <A>mode</A>.)
##  <P/>
##  <M>G</M> must be an &ATLAS; group, and the classes of <A>tbl</A> must be
##  sorted compatibly with the
##  &ATLAS; of Finite Groups&nbsp;<Cite Key="CCN85"/>,
##  </Description>
##  </ManSection>
##
DeclareGlobalFunction( "StringOfAtlasProgramCycToCcls" );


#############################################################################
##
#F  CurrentDateTimeString( [<options>] )
##
##  <ManSection>
##  <Func Name="CurrentDateTimeString" Arg='[options]'/>
##
##  <Description>
##  If the system function <C>date</C> is available then the return value is
##  a string that describes the current date and time,
##  otherwise the string <C>"unknown"</C> is returned.
##  <P/>
##  If the argument <A>options</A> is given it must be a list of options for
##  <C>date</C>;
##  for example an empty list means the local time,
##  and the value <C>[ "-u" ]</C> means Greenwich mean time (UTC).
##  <P/>
##  If no argument is given then the format of the result refers to Greenwich
##  mean time and is compatible with <Ref Func="StringDate" BookName="ref"/>
##  and <Ref Func="StringTime" BookName="ref"/>;
##  in this case the option <C>+%s</C> is used.
##  </Description>
##  </ManSection>
##
DeclareGlobalFunction( "CurrentDateTimeString" );


#############################################################################
##
#F  SendMail( <sendto>, <copyto>, <subject>, <text> )
##
##  <ManSection>
##  <Func Name="SendMail" Arg='sendto, copyto, subject, text'/>
##
##  <Description>
##  Let <A>sendto</A> and <A>copyto</A> be lists of email addresses,
##  and <A>subject</A> and <A>text</A> be strings.
##  <Ref Func="SendMail"/> sends email messages with subject <A>subject</A>
##  and body <A>text</A> to the addresses in <A>sendto</A> and <A>copyto</A>.
##  </Description>
##  </ManSection>
##
DeclareGlobalFunction( "SendMail" );


#############################################################################
##
#F  ParseBackwards( <string>, <format> )
#F  ParseBackwardsWithPrefix( <string>, <format> )
#F  ParseForwards( <string>, <format> )
#F  ParseForwardsWithSuffix( <string>, <format> )
##
##  <ManSection>
##  <Func Name="ParseBackwards" Arg='string, format'/>
##  <Func Name="ParseBackwardsWithPrefix" Arg='string, format'/>
##  <Func Name="ParseForwards" Arg='string, format'/>
##  <Func Name="ParseForwardsWithSuffix" Arg='string, format'/>
##
##  <Description>
##  <!--  Remove this as soon as <C>gpisotyp</C> is available!-->
##  </Description>
##  </ManSection>
##
DeclareGlobalFunction( "ParseBackwards" );
DeclareGlobalFunction( "ParseBackwardsWithPrefix" );
DeclareGlobalFunction( "ParseForwards" );
DeclareGlobalFunction( "ParseForwardsWithSuffix" );


#############################################################################
##
#F  AtlasRepIdentifier( <oldid> )
#F  AtlasRepIdentifier( <id>, "old" )
##
##  <#GAPDoc Label="AtlasRepIdentifier">
##  <ManSection>
##  <Heading>AtlasRepIdentifier</Heading>
##  <Func Name="AtlasRepIdentifier" Arg='oldid'
##   Label="convert an old type identifier to a new type one"/>
##  <Func Name="AtlasRepIdentifier" Arg='id, "old"'
##   Label="convert a new type identifier to an old type one"/>
##
##  <Description>
##  This function converts between the <Q>old format</Q> (the one used up to
##  version 1.5.1 of the package) and the <Q>new format</Q> (the one used
##  since version 2.0) of the <C>identifier</C> component of the records
##  returned by &AtlasRep; functions.
##  Note that the two formats differ only for <C>identifier</C> components
##  that describe data from non-core parts of the database.
##  <P/>
##  If the only argument is a list <A>oldid</A> that is an <C>identifier</C>
##  in old format then the function returns the corresponding
##  <C>identifier</C> in new format.
##  If there are two arguments, a list <A>id</A> that is an <C>identifier</C>
##  in new format and the string <A>"old"</A>,
##  then the function returns the corresponding <C>identifier</C> in old
##  format if this is possible, and <K>fail</K> otherwise.
##  <P/>
##  <Example><![CDATA[
##  gap> id:= [ "A5", [ "A5G1-p5B0.m1", "A5G1-p5B0.m2" ], 1, 5 ];;
##  gap> AtlasRepIdentifier( id ) = id;
##  true
##  gap> id:= [ "L2(8)", "L28G1-check1", 1, 1 ];;
##  gap> AtlasRepIdentifier( id ) = id;
##  true
##  gap> oldid:= [ [ "priv", "C4" ], [ "C4G1-p4B0.m1" ], 1, 4 ];;
##  gap> newid:= AtlasRepIdentifier( oldid );
##  [ "C4", [ [ "priv", "C4G1-p4B0.m1" ] ], 1, 4 ]
##  gap> oldid = AtlasRepIdentifier( newid, "old" );
##  true
##  gap> oldid:= [ [ "priv", "C4" ], "C4G1-max1W1", 1 ];;
##  gap> newid:= AtlasRepIdentifier( oldid );
##  [ "C4", [ [ "priv", "C4G1-max1W1" ] ], 1 ]
##  gap> oldid = AtlasRepIdentifier( newid, "old" );
##  true
##  gap> oldid:= [ [ "priv", "C4" ], "C4G1-Ar1aB0.g", 1, 1 ];;
##  gap> newid:= AtlasRepIdentifier( oldid );
##  [ "C4", [ [ "priv", "C4G1-Ar1aB0.g" ] ], 1, 1 ]
##  gap> oldid = AtlasRepIdentifier( newid, "old" );
##  true
##  gap> oldid:= [ [ "priv", "C4" ], "C4G1-XtestW1", 1 ];;
##  gap> newid:= AtlasRepIdentifier( oldid );
##  [ "C4", [ [ "priv", "C4G1-XtestW1" ] ], 1 ]
##  gap> oldid = AtlasRepIdentifier( newid, "old" );
##  true
##  gap> oldid:= [ [ "mfer", "2.M12" ],
##  >  [ "2M12G1-p264aB0.m1", "2M12G1-p264aB0.m2" ], 1, 264 ];;
##  gap> newid:= AtlasRepIdentifier( oldid );
##  [ "2.M12", 
##    [ [ "mfer", "2M12G1-p264aB0.m1" ], [ "mfer", "2M12G1-p264aB0.m2" ] ]
##      , 1, 264 ]
##  gap> oldid = AtlasRepIdentifier( newid, "old" );
##  true
##  ]]></Example>
##  </Description>
##  </ManSection>
##  <#/GAPDoc>
##
DeclareGlobalFunction( "AtlasRepIdentifier" );


#############################################################################
##
#F  CompositionOfSLDAndSLP( <sld>, <slp> )
##
##  <ManSection>
##  <Func Name="CompositionOfSLDAndSLP" Arg='sld, slp'/>
##
##  <Description>
##  Return a straight line decision that first applies the straight line
##  program <A>slp</A> to its inputs and then returns the result of the
##  straight line decision <A>sld</A> on the outputs.
##  <P/>
##  A typical situation is that <A>slp</A> is a restandardization script
##  and <A>sld</A> is a presentation.
##  </Description>
##  </ManSection>
##
DeclareGlobalFunction( "CompositionOfSLDAndSLP" );


#############################################################################
##
#F  AtlasRepComputedKernelGenerators( <gapname>, <std>,
#F                                    <factgapname>, <factstd>,
#F                                    <bound> )
##
##  <ManSection>
##  <Func Name="AtlasRepComputedKernelGenerators"
##   Arg='gapname, std, factgapname, factstd, bound'/>
##
##  <Description>
##  We assume that <A>gapname</A> and <A>factgapname</A> are valid arguments 
##  of <Ref Func="AtlasGroup"/>,
##  and that the <A>std</A>-th and <A>factstd</A>-th standard generators of
##  the two groups <M>G</M> and <M>F</M>, say, are compatible
##  in the sense that mapping the generators of <M>G</M> to those of <M>F</M>
##  defines an epimorphism.
##  <P/>
##  If representations for the two groups in the given standardizations
##  are locally available then the following happens.
##  <P/>
##  The function runs over the elements of a free monoid and collects those
##  elements that evaluate to elements of different orders in the two groups
##  and thus lie in the kernel of the epimorphism from <M>G</M> to <M>F</M>.
##  Only those words in the free generators are considered for which the
##  exponents of all syllables are smaller than the orders of the
##  corresponding generators of <M>G</M>.
##  <P/>
##  If <A>gapname</A> and <A>factgapname</A> are two identifiers of
##  character tables from the &GAP; Character Table Library such that 
##  a factor fusion from the table of <A>gapname</A> to that of 
##  <A>factgapname</A> is stored then the character tables are used 
##  to determine those orders of elements in <A>F</A> for which a preimage 
##  in <M>G</M> has larger order.
##  In this case, only those elements of <M>G</M> are computed for which 
##  the order of the corresponding element of <M>F</M> admits a preimage of
##  larger order in <M>G</M>.
##  <P/>
##  At most the first <A>bound</A> words in the free generators are checked
##  for which an element of <M>G</M> is actually computed according to these 
##  rules.
##  <P/>
##  The function returns <K>fail</K> if it finds out that the generators
##  are not compatible;
##  in this case, a message about the details is printed
##  if the info level of <Ref Var="InfoAtlasRep"/> is at least <M>3</M>.
##  Otherwise, the function returns a list <M>[ l, flag ]</M>,
##  where <M>l</M> is a list of pairs <M>[ w, o ]</M> such that <M>w^o</M>
##  describes an element in the kernel,
##  and <M>flag</M> is <K>true</K> if these words are known to generate
##  the kernel, and <K>false</K> otherwise.
##  <P/>
##  Yes, the strategy used is quite simpleminded:
##  First, although the words in the free monoid are checked in an ordering
##  that respects the length of the words, it may happen that some longer
##  word can be evaluated with a straight line program that needs less
##  multiplications.
##  Second, the checks of many words are unnecessary because these words
##  evaluate to the same elements as words that have been checked already.
##  <P/>
##  Moreover, the strategy is suitable only for computing <E>small</E>
##  kernels, since membership tests for the kernel are needed if it is not
##  cyclic.  Large kernels occur for example in maximal subgroups of the
##  Monster group; if such a kernel is an irreducible module then it is
##  a better approach to find one nontrivial element in the kernel and
##  suitable conjugating elements of the maximal subgroup.
##  <P/>
##  <Example><![CDATA[
##  gap> AtlasRepComputedKernelGenerators( "2.A5", 1, "A5", 1, 10^6 );
##  [ [ [ m1, 2 ] ], true ]
##  gap> g:= AtlasGroup( "A5" );;
##  gap> 2g:= AtlasGroup( "2.A5" );;
##  gap> List( GeneratorsOfGroup( g ), Order );
##  [ 2, 3 ]
##  gap> List( GeneratorsOfGroup( 2g ), Order );
##  [ 4, 3 ]
##  ]]></Example>
##  </Description>
##  </ManSection>
##
DeclareGlobalFunction( "AtlasRepComputedKernelGenerators" );


#############################################################################
##
#E