Question 1119185
<pre>
1. R v ~S                      Premise
2. ~R v T                      Premise
3. T —> (S • U)                Premise
4. R—>T                        2, Relation of Implication (IMPL)
5. ~S v R                      1, Commutative property (COMM)
6. S—>R                        5, IMPL
7.  S—>T                       6,4, Rule of Syllogism (SYL)
8.  T—>S                       3, AND elimination
9.  S <—> T                    7,8  BiConditional introduction (BI).    Done.