Question 199021
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1. ( R * S) v (R * ~E)		    Pr.
2. (Y * O) -> (E * ~S)		    Pr.
3. (O -> ~Y) -> L 		    Pr. / .: L
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4.   R * (S v ~E)                   1            Distribution
5.   (S v ~E) * R                   4            Commutation
6.   S v ~E                         5            Simplification
7.   ~E v S                         6            Commutation
8.   ~E v ~~S                       7            Double Negation
9.   ~(E * ~S)                      8            De Morgan's Law
10.  ~(Y * O)                     2,9            Modus Tollens
11.  ~Y v ~O                       10            De Morgan's Law
12.  ~O v ~Y                       11            Commutation
13.  O -> ~Y                       12            Material Implication
14.  L                           3,13            Modus Ponens
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