[GAP Forum] A question about Action

[Peter Cameron]

Dear GAP forum,

It seems that GAP can find representatives for all systems of minimal blocks
of imprimitivity for an arbitrary group action, but all blocks only for a
permutation group (and there seems no easy way to get all maximal blocks).

I have tried to get around this as follows. G is a group acting on O (which
is actually an orbit on 2-subsets of [1..n]). I do the following:

GG:=Action(G,O,OnSets);
BB:=AllBlocks(GG);
B:=List(BB,x->List(x,y->O[y]));

This assumes that the Action maps each element of O to its position in the
list, and I can't find a guarantee to this effect in the manual. Can I rely
on this?

Thanks for any advice.

Peter Cameron.



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