proposition: Lemma oddE n: odd n -> n = (n./2).*2.+1.
proof: Proof. by rewrite -{2} (odd_double_half n) => ->. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path fintype div bigop binomial) mathcomp(prime finset ssralg ssrnum ssrint)