47.20 IdempotentsTom

IdempotentsTom( tom )

IdempotentsTom returns the list of idempotents of the integral Burnside ring described by the table of marks tom. According to A.~Dress Dre69, these idempotents correspond to the classes of perfect subgroups, and each such idempotent is the characteristic function of all those subgroups which arise by cyclic extension from the corresponding perfect subgroup.

    gap> IdempotentsTom( a5 );
    [ 1, 1, 1, 1, 1, 1, 1, 1, 9 ] 

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