[GAP Forum] Fwd: [GAP Support] Suggested response: RepresentativeAction gives error

[Alexander Hulpke]

Dear GAP-Forum,

Andrew Johnson reported a bug in `RepresentativeAction' for  
subgroups. Thank you very much.
This error will be corrected in the next bugfix.

Before going into details of the bug in question, let me take this  
opportunity to remind everyone of the existence of the email address  
support at gap-system.org, which is intended for bug reports or to  
request help with installation problems. The forum email list goes to  
several hundred people worldwide, most of whom likely are not  
interested in lengthy error descriptions or stack dumps.

Now to the bug in question. What happens is that the conjugacy test  
in permutation groups contains a special treatment for groups with an  
elementary abelian regular subgroup (EARNS), as such groups are  
important in the classification of primitive groups. What is missing  
is the (easy) check that not just one, but both groups have an EARNS.  
In the example this was not the case, the error was triggered when  
trying to use the  EARNS of group2. (You can verify this by swapping  
group2 and group1.)
As mentioned this will be corrected in the next bugfix.

In case you are testing a larger set of subgroups of S_n (for n<=31)  
for conjugacy, you might want to look as well as the command  
`TransitiveIdentification', which uses the classification of  
transitive subgroups of the symmetric group (known up to degree 31)  
and which is likely to be much faster.

Best wishes,

     Alexander Hulpke


-- Colorado State University, Department of Mathematics,
Weber Building, 1874 Campus Delivery, Fort Collins, CO 80523-1874, USA
email: hulpke at math.colostate.edu, Phone: ++1-970-4914288
http://www.math.colostate.edu/~hulpke