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Dear Gordon and GAP Forum,

On Tue, Apr 29, 2003 at 09:32:55AM +0800, Gordon Royle wrote: > Hi, > > I am having great problems searching for certain subgroups... > > Here is a group: > > g001 := PermList([1,2,3,4,9,10,11,12,5,6, > 7,8,13,14,15,16,17,18,19,20, > 25,26,27,28,21,22,23,24,29,30, > 31,32,33,34,35,36,41,42,43,44, > 37,38,39,40,45,46,47,48,49,50, > 51,52,57,58,59,60,53,54,55,56, > 61,62,63,64]); > ... > g := GroupWithGenerators([g001,g002,g003,g004,g005]); > > I know that it has an elementary abelian normal subgroup of order 64... > > But when I try to find it, this happens.. > > gap> n := NormalSubgroups(g); > Error <obj> is not a subset of the parent of <G> at > Error( "<obj> is not a subset of the parent of <G>" ); > ClosureSubgroup( b, k ) called from > SubgroupsSolvableGroup( r, rec( > actions := auts, > funcnorm := r, > consider := ExactSizeConsiderFunction( Index( j, M ) ), > normal := true ) ) called from > <function>( <arguments> ) called from read-eval-loop > Entering break read-eval-print loop, you can 'quit;' to quit to outer > loop, > or you can return to continue >

This diagnostic suggests to me that you are still using some version

of GAP 4.2 or perhaps even an earlier version. The current version of

GAP is GAP 4.3fix4.

Trying your command I got the following:

gap> n := NormalSubgroups(g);

[ <permutation group of size 24576 with 5 generators>,

<permutation group with 13 generators>,

<permutation group with 12 generators>,

<permutation group with 10 generators>,

<permutation group with 10 generators>,

<permutation group with 10 generators>,

<permutation group with 8 generators>,

<permutation group with 13 generators>,

<permutation group with 13 generators>,

<permutation group with 12 generators>,

<permutation group with 11 generators>,

<permutation group with 9 generators>, <permutation group with 9 generators>

, <permutation group with 9 generators>,

<permutation group with 7 generators>, <permutation group with 7 generators>

, <permutation group with 7 generators>,

<permutation group with 7 generators>, <permutation group with 7 generators>

, <permutation group with 5 generators>,

<permutation group with 6 generators>, <permutation group with 4 generators>

, <permutation group with 6 generators>,

<permutation group with 6 generators>, <permutation group with 4 generators>

, <permutation group with 4 generators>,

<permutation group with 3 generators>, <permutation group with 3 generators>

, <permutation group with 3 generators>,

<permutation group with 2 generators>, Group(()) ]

What am I doing wrong? I read the manual, but cannot see any

pre-conditions

for the "NormalSubgroups" routine that I am violating...

It looks as if you have struck a bug in an older GAP that has since been

fixed. Could you please upgrade your installation to the current version

of GAP.

BTW You will need to get the latest version from either the St Andrews

or Aachen sites (the ANU mirror is no longer maintained). Go to:

http://www.gap-system.org (for St Andrews)

Regards,

Greg Gamble

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