Question 588387
Unfortunately you also made a mistake in line 16. Here's one way to derive the conclusion.


<pre>
1.  X > Y             / (X . Z) > Y
-------------------------
2.  ~X v Y                  1       Material Implication
3.  (~X v Y) v ~Z           2       Addition
4.  ~X v (Y v ~Z)           3       Association
5.  ~X v (~Z v Y)           4       Commutation
6.  (~X v ~Z) v Y           5       Association
7.  ~(X . Z) v Y            6       De Morgan's Law
8.  (X . Z) > Y             7       Material Implication
</pre>