proposition: Lemma subf_div1 x y: y != 0 -> 1 - x / y = (y - x) /y.
proof: Proof. by move => h; rewrite -mulNr addf_div1 // addrC. Qed.
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)