proposition: Lemma fib3S n: fib n.+3 = (fib n.+1).*2 + (fib n).
proof: Proof. by rewrite fibSS fibSS addnAC addnn. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path fintype div bigop binomial) mathcomp(prime finset ssralg ssrnum ssrint)