proposition: Lemma catalan_SSn n: 0 < n -> catalan n.+1 = 'C(n.*2.+1, n.+1) - 'C(n.*2.+1, n.-1).
proof: Proof. by move => h; rewrite catalan_pos // doubleS /= (bin_fact2n_f h). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype) mathcomp(ssrnat seq path div) mathcomp(fintype tuple finfun bigop finset binomial)