1. P v Q
2. P → (T → S),
3. P → T,
4. S ↔ Q ├ S
|5. ~S Assumption for Indirect Proof
|6. (S → Q) & (Q → S) 4, Material Equivalence
|7. (Q → S) & (S → Q) 6, Commutation
|8. Q → S 7, Simplification
|9. ~Q 8,5, Modus Tollens
|10. Q v P 1, Commutation
|11. P 10,9, Disjunctive Syllogism
|12. T 3,11, Modus Ponens
|13. T → S 2,11, Modus Ponens
|14. S 13,12, Modus Ponens
|15. ~S & S 5,14, Conjunction
16. S Lines 5-15 Indirect Proof
Edwin