fact: Definition sub n (x y : obstring n) := match x, y with | Some (exist _ s _), Some (exist _ t _) => s <> t /\ exists s', t = s'++s | _, _ => False end.
imports: Lia Arith Undecidability.PCP.PCP Undecidability.PCP.Util.PCP_facts Undecidability.Synthetic.DecidabilityFacts Undecidability(FOL.Utils.FullSyntax) Undecidability(FOL.FSAT) Undecidability.Shared.ListAutomation