Question 1090916
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1. U v (~U > ~B) 
2. ~B > (R > U)
3. ~U           / ~R

4. ~U > ~B          1,3, Disjunctive Syllogism
5. ~B               4,3, Modus Ponens
6. R > U            2,5, Modus Ponens
7. ~R               6,3, Modus Tollens

Edwin</pre>