proposition: Lemma cast_permKV m n eq_m_n : cancel (cast_perm (esym eq_m_n)) (@cast_perm m n eq_m_n).
proof: Proof. by subst m. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)