proposition: Lemma fusc_even n: fusc n.*2 = fusc n.
proof: Proof. by move: fusc_rec => []. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq choice fintype order bigop ssralg) mathcomp(div ssrnum ssrint rat prime path binomial) mathcomp(tuple finset) gaia(fibm)