Question 277572
You made a mistake on line 11. You should have P v Z (not P v S) since the consequent of U -> Z is Z



So continuing with your work...


<pre>
11.  P v Z                     2,4,10      Constructive Dilemma
12.  ~M                        7,11        Modus Ponens
13.  ~S                        5,12        Modus Tollens
14.  ~Y                        6,13        Disjunctive Syllogism

</pre>