proposition: Lemma F38 n: \sum_(i<n.+1) 'C(n,i) ^2 = 'C(n.*2, n).
proof: Proof. rewrite - addnn - (F36 n n n); apply: congr_big => // [[i isn]]. by rewrite expnS expn1 bin_sub //. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype) mathcomp(ssrnat seq path div) mathcomp(fintype tuple finfun bigop finset binomial)