I'm struggling a bit with these formulas, whether they are tautologies or not;
1)
2)
Any help/tips on where to start/solve these would be greatly appreciated!
1.
2. (by deduction theorem)
3. (by rule EI, existential instantiation)
4. (by generalization theorem)
5. (by generalization theorem)
6. (contraposition)
7. (quantifier axiom)
Thus, (2) is tautology.