The following are three valid arguments. Establish the validity of each by means of a truth table. In each case, determine which rows of the table are crucial for assessing the validity of the argument and which rows can be ignored.
a) [p ∧ (p→q) ∧ r] → [(p ∨ q)→r]
b) [[(p ∧ q)→r] ∧ ￢q ∧ (p→￢r)]→(￢p ∨￢q)
c) [[p ∨ (q ∨ r)] ∧ ￢q]→(p ∨ r)