I double-checked this, and it is in fact a bug in GAP (GAP 4.10).
gap> for A in AllPrimitiveGroups( DegreeOperation,[3]) do
> for G in NormalSubgroups(A) do
> for U in ConjugacyClassesSubgroups(G) do
> P := TrivialCharacter(Representative(U));
> for x in ConjugacyClassesSubgroups(G) do
> Print("x=", x, "\n");
> for y in ConjugacyClassesSubgroups(Representative(x)) do
> Print(y);
> od;od;od;
> od;od;
x=ConjugacyClassSubgroups(A(3),Group( () ))
Error, usage: FreeGroup(<name1>,<name2>..) or FreeGroup(<rank>) at
/home/dimpase/sage/local/share/gap/lib/grpfree.gi:467 called from
FreeGroup( deg - 1, nam ) at
/home/dimpase/sage/local/share/gap/lib/gpprmsya.gi:1753 called from
IsomorphismFpGroup( G, Concatenation( "S_", String( Length(
MovedPoints( G ) ) ), "." ) ) at
/home/dimpase/sage/local/share/gap/lib/gpprmsya.gi:1729 called from
IsomorphismFpGroup( Image( hom ) ) at
/home/dimpase/sage/local/share/gap/lib/grplatt.gi:890 called from
LatticeSubgroups( G ) at
/home/dimpase/sage/local/share/gap/lib/grplatt.gi:208 called from
ConjugacyClassesSubgroups( Representative( x ) ) at *stdin*:36 called from
... at *stdin*:39
you can 'quit;' to quit to outer loop, or
you can 'return;' to continue
brk>
On Sat, Aug 15, 2020 at 12:13 AM Dima Pasechnik <dimp...@gmail.com> wrote:
>
> it is not libgap, it is pexpect GAP that is used here - something we should
> get rid of.
>
>
> On Fri, 14 Aug 2020, 23:39 'Peter Mueller' via sage-support,
> <sage-support@googlegroups.com> wrote:
>>
>> The following code yields a Traceback for no (to me) obvious reason. The
>> same happens on sagecell too. It seems to be a minimal case. For instance
>> removing the line "P = ..." or having less deeply nested loops does not
>> display this problem:
>>
>> for A in PrimitiveGroups(3):
>> for G in A.normal_subgroups():
>> for U in G.conjugacy_classes_subgroups():
>> P = U.trivial_character()
>> for x in G.conjugacy_classes_subgroups():
>> for y in x.conjugacy_classes_subgroups():
>> pass
>>
>> GAPError Traceback (most recent call last)
>> <ipython-input-1-c79c371f18a8> in <module>()
>> ----> 1 load('./bug2.sage')
>>
>> /home/mueller/local/sage-9.1/local/lib/python3.7/site-packages/sage/misc/persist.pyx
>> in sage.misc.persist.load (build/cythonized/sage/misc/persist.c:2538)()
>> 142
>> 143 if sage.repl.load.is_loadable_filename(filename):
>> --> 144 sage.repl.load.load(filename, globals())
>> 145 return
>> 146
>> [.................. SNIP .....................]
>> > 2514 sig_on()
>> 2515 if n == 0:
>> 2516 result = CALL_0ARGS(self.value)
>>
>> GAPError: Error, usage: FreeGroup(<name1>,<name2>..) or FreeGroup(<rank>)
>>
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