fact: Variables (gT rT : finGroupType) (D G : {group gT}) (f : {morphism D >-> rT}).
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div) mathcomp(fintype bigop prime finset fingroup morphism) mathcomp(perm action quotient gproduct cyclic center) mathcomp(pgroup nilpotent sylow hall abelian)