LOGIC. Show if the inferences corresponding to the following formulas
are valid or not:
a) {[(p ∨ q) → (r ∨ s)] & [(r ∨ t) → s]}
→ (p → s)
b) {{(p & q) → [r → (s & t)]} & [(q ∨ u)
→ (r & ¬s] & (p → q)}→ ¬p
c) {[(p & q) ∨ (r & s)] & [q → (t & u)]
& [s → (m & n)]} → (u ∨ n)
d) {[(p ∨ q) → (r ∨ s)] & [r → (s & t)]
& [(t ∨ u) → v]} → (p → v)
e) {[p → (q ∨ r)] & [q → (s ∨ t)] &
[r → (u ∨ s)] & [(u ∨ t) → s]}
→ (p → s)