fact: Definition prefix s1 s2 : Prop := forall n x, onth s1 n = some x -> onth s2 n = some x.
imports: Coq(ssreflect ssrbool ssrfun Eqdep) mathcomp(ssrnat seq eqtype choice fintype) pcm(options axioms) Coq(Classes.Morphisms Program.Basics Program.Tactics) Coq(Relations)