proposition: Lemma nbder_even_gt0 n: ~~ odd n -> 0 < nder n.
proof: Proof. case:n => // [] // [] // n _; apply: nbder_gt0 n. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype) mathcomp(ssrnat seq path div) mathcomp(fintype tuple finfun bigop finset binomial)