proposition: Lemma commMgR x y z : [~ x * y, z] = [~ x, z] * [~ x, z, y] * [~ y, z].
proof: Proof. by rewrite commMgJ conjg_mulR. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat fintype) mathcomp(bigop finset binomial fingroup morphism) mathcomp(automorphism quotient gfunctor)