proposition: Lemma Sd1_inj : injective Sd1.
proof: Proof. by apply: can_inj Sd1 _; case; do 4?case=> //=; move=> H; apply/eqP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype tuple finfun bigop finset fingroup) mathcomp(action perm primitive_action)