proposition: Lemma lin_app S1 S2 t: lin (S1 ++ S2) t = lin S1 (lin S2 t).
proof: Proof. unfold lin; simplify; now rewrite AppL_app. Qed.
imports: RelationClasses Morphisms List Lia Init.Nat Setoid Undecidability.HOU(calculus.calculus second_order.diophantine_equations systemunification nth_order_unification)