Question 1171842
<pre>
No, 4 should be ~O by disjunctive syllogism, and then ~T by 1 and 4 and Modus Tollens.

1. T ⊃ O
2. R v ~O
3. ~R           /~T

4. ~O       2,3   Disjunctive syllogism
5. ~T       1,4   Modus Tollens 

Edwin</pre>