proposition: Lemma card_modular_group : #|'Mod_(p ^ n)| = (p ^ n)%N.
proof: Proof. by rewrite Extremal.card def_p ?def_q // -expnS def_n. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset prime binomial) mathcomp(fingroup morphism perm automorphism presentation) mathcomp(quotient action commutator gproduct gfunctor) mathcomp(ssralg countalg finalg zmodp cyclic pgroup center gseries) mathcomp(nilpotent sylow abelian finmodule matrix maximal)