fact: Fixpoint Fib_fusc_rec n := if n is m.+1 then let (a,b):= Fib_fusc_rec m in (b.*2.+1, a + b) else (0,0).
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)