fact: Definition Side_eq x y := match x, y with LL, LL => true | RR, RR => true | _, _ => false end.
imports: Coq(ssreflect ssrbool ssrfun Eqdep) mathcomp(ssrnat seq eqtype choice fintype) pcm(options axioms) Coq(Classes.Morphisms Program.Basics Program.Tactics) Coq(Relations)