A propositional formula is called a tautology if it evaluates to 1 for all possible values of its variables, a contradiction if it always evaluates to 0, and a contingency otherwise. Classify each expression below as tautology/contradiction/contingency (enter the full word as your answer). For those that are tautologies or contradictions, can you see why this is the case without using a truth table or simplifying the expression? tautology/contradiction/contingency Expression (PVQ) Q (PAQ) P (PQ) A (P=(-Q))) AP ( PR) ( QP) P=(QP)