proposition: Lemma pcoreNK pi G : 'O_pi^'^'(G) = 'O_pi(G).
proof: Proof. by apply: eq_pcore; apply: negnK. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(fintype bigop finset prime fingroup morphism) mathcomp(gfunctor automorphism quotient action gproduct) mathcomp(cyclic)