proposition: Lemma reachable_n_trans' {M} n {m k X X' Y Z} : m+n <= k -> X = X' -> reachable_n M n Y Z -> reachable_n M m X Y -> reachable_n M k X' Z.
proof: Proof. move /reachable_n_mon => H *. subst. apply: H. by apply: reachable_n_trans; eassumption. 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