Proof (vagree_bitwise_binop Int.or (iagree_bitwise_binop orb Int.or Int.bits_or)).

Lemma xor_sound:
forall v1 w1 v2 w2 x,
vagree v1 w1 (bitwise x) -> vagree v2 w2 (bitwise x) ->
vagree (Val.xor v1 v2) (Val.xor w1 w2) x.