fact: Definition Fib_fusc_sym n := 3*2^(n.-2) - (Fib_fusc_rec n).1.
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)