Which of the following logical expressions are tautologies?
P∨¬PP \lor \neg PP∨¬P
P∧¬PP \land \neg PP∧¬P
P→(Q→P)P \rightarrow (Q \rightarrow P)P→(Q→P)
P→(P∧Q)P \rightarrow (P \land Q)P→(P∧Q)