proposition: Lemma quotient1_isog : isog A (A / 1).
proof: Proof. by apply: isom_isog quotient1_isom; apply: norms1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)