proposition: Lemma binom_mn_n m n : 'C(m + n, m) = 'C(m + n, n).
proof: Proof. by have:= (bin_sub (leq_addl m n)); rewrite addnK. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype) mathcomp(ssrnat seq path div) mathcomp(fintype tuple finfun bigop finset binomial)