proposition: Lemma IFR_then : P -> (IF P then x else y) == x.
proof: Proof. by move=> haveP; case: IFR_cases => z [][]. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div order) mathcomp(ssralg ssrnum ssrint rat intdiv) Coq(Morphisms Setoid) fourcolor(real realsyntax)