fact: Definition pHall pi A B := [&& B \subset A, pgroup pi B & pi^'.-nat #|A : B|].
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(fintype bigop finset prime fingroup morphism) mathcomp(gfunctor automorphism quotient action gproduct) mathcomp(cyclic)