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