Hello fine. I'm studying logic and great difficulties to understand its principles, and should prove some theories involving the laws of identity of sets of mathematics using the method of natural deduction, they are: a) A ∪ ∅ = A b) A ∩ ∅ = ∅ I am trying as follows, but I can not solve http://www.imagesup.net/dm-1514135726215.png [Broken] Could anyone help me solve ?! If I could be pointed out to me some book or website to get more doubts which were to appear on deduction of sets I'd appreciate it. Thank you.