fact: Definition pprodm of B \subset 'N(A) & {in A & B, morph_act 'J 'J fA fB} & {in A :&: B, fA =1 fB} := fun x => fA (divgr A B x) * fB (remgr A B x).
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)