1 Logical equivalence - luc.edu
gauss.math.luc.edu › greicius › Math201When we rst de ned what P ,Q means, we said that this equivalence is true if P )Q is true and the converse Q )P is true. This is in fact a consequence of the truth table for equivalence. So one way of proving P ,Q is to prove the two implications P )Q and Q )P. Example. Let n be an integer. Prove that n2 is odd if and only if n is odd. We must prove TWO implications, P )Q and Q )P.