proposition: Lemma rcoset_trans x y z : x \in G :* y -> y \in G :* z -> x \in G :* z.
proof: Proof. by move/rcoset_transl->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)