, prove that 3. Let be an alphabet. For any strings u, v E (a) uv = u + lul. (b) |uv = (vul. 4. Let be an alphabet. Consider strings u, v, W E . Prove that the concatenation operation is associative (i.e. (v)w = u(vw)). , prove that 3. Let be an alphabet. For any strings u, v E (a) uv = u + lul. (b) |uv = (vul. 4. Let be an alphabet. Consider strings u, v, W E . Prove that the concatenation operation is associative (i.e. (v)w = u(vw))