proposition: Lemma maybe_reachable_refl' {M n X Y} : X = Y -> maybe_reachable M n X Y.
proof: Proof. move=> ->. left. by apply: reach_refl. Qed.
imports: List Lia Relation_Operators Undecidability.StackMachines.Util(Nat_facts List_facts) Undecidability.StackMachines.Reductions.CM1_HALT_to_SMNdl_UB.SMX ssreflect ssrbool ssrfun