proposition: Lemma fib_doubleS n: fib (n.*2.+1) = fib n.+1 ^ 2 + fib n ^ 2.
proof: Proof. by rewrite -addnn -addSn fib_add // addnC. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path fintype div bigop binomial) mathcomp(prime finset ssralg ssrnum ssrint)