fact: Definition semiprime K H := {in H^#, forall x, 'C_K[x] = 'C_K(H)}.
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)