proposition: Lemma fib_ge2_alt n: fib n.+3 = (fib n.+3).-2.+2.
proof: Proof. by rewrite - (subnK(fib_gen (n.+2))) 2!addnS. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path fintype div bigop binomial) mathcomp(prime finset ssralg ssrnum ssrint)