Show that resolution is commutative and associative. Specifically, if A, B, and C are Horn clauses, show that (A ⊕B) = (B ⊕ A) and that ((A ⊕ B) ⊕ C) = (A ⊕ (B ⊕ C)), where ⊕ indicates resolution. Be sure to think about what happens to variables that are instantiated as a result of unification.