fact: Fixpoint SB_to_rat x := match x with xH => 1 | xO x' => Sba_i (SB_to_rat x') | xI x' => Sba_p (SB_to_rat x') end.
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)