proposition: Lemma reachable_n_refl' {M n X X'} : X = X' -> reachable_n M n X X'.
proof: Proof. move=> ->. 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