proposition: Lemma fib_pos n: fib (n.+1) = (fib (n.+1)).-1.+1.
proof: Proof. by rewrite prednK // fib_gt0 //. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path fintype div bigop binomial) mathcomp(prime finset ssralg ssrnum ssrint)