Unformatted text preview: are both false. By inspection of the truthtable, this seems less likely to be possible since there is only one combination of truth values of p and q which makes p = ⇒ q false. We now prove that it is, in fact, impossible to Fnd such propositions. Proof. By contradiction, suppose that there were propositions p and q such that p = ⇒ q is false and q = ⇒ p is also false. Since p = ⇒ q is false, it must be the case that p is true and q is false (by the third line of the truthtable). Similarly, since q = ⇒ p is false, q is true and p is false. Thus, p must be both true and false, which is impossible. We arrived at contradiction when we assumed that there were such propositions so we conclude that there are no propositions where the implication and its converse are both false. ±...
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This note was uploaded on 08/02/2011 for the course MATH 109 taught by Professor Knutson during the Spring '06 term at UCSD.
 Spring '06
 Knutson
 Math

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