[GAP Forum] problem with Stabilizer

Michael Hartley Michael.Hartley at nottingham.edu.my
Fri Jul 2 07:19:22 BST 2004

Dear Forum,

What am I doing wrong here?? 

The following commands (given to Gap 4.3fix5)

grp := AlternatingGroup(7);
aut := AutomorphismGroup(grp);
stb := Stabilizer(aut,(3,4)(5,6));

lead to this error :
------- begin GAP output---------
GAP4, Version: 4.3fix5 of June, 2003, i686-pc-cygwin-gcc
Components:  small, small2, small3, small4, small5, small6, small7,
             small8, id2, id3, id4, id5, id6, trans, prim  loaded.
Packages:    crisp, cryst, polycyclic, crystcat, ctbllib, tomlib,
             EDIM, GAPDoc, factint, lag  loaded.
gap> grp := AlternatingGroup(7);
Alt( [ 1 .. 7 ] )
gap> aut := AutomorphismGroup(grp);
<group with 3 generators>
gap> stb := Stabilizer(aut,(3,4)(5,6));
Error, no method found! For debugging hints type ?Recovery from
Error, no 2nd choice method found for
`ConjugatorOfConjugatorIsomorphism' on 1\
 arguments called from
ConjugatorOfConjugatorIsomorphism( auto ) called from
map!.fun( elm ) called from
ImagesRepresentative( nice, obj2 ) called from
ClosureGroup( G, obj ) called from
ClosureSubgroupNC( stb, sch ) called from
Entering break read-eval-print loop ...
you can 'quit;' to quit to outer loop, or
you can 'return;' to continue
----------end GAP output-----------

The error depends sensitively on the group, even on the order of its
generators! Eg, if the first line is replaced with any of 

grp := AlternatingGroup(6);


grp := AlternatingGroup(8);

or even (!)

grp := Group(GeneratorsOfGroup(AlternatingGroup(7)));

allows the Stabilizer function to finish normally.

Can this be fixed by merely upgrading to the current latest version of
GAP? Or is there a workaround in my version? Or must I wait for a future

Yours, Mike H...

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