Discrete Mathematics and Its Applications, Seventh Edition

Published by McGraw-Hill Education
ISBN 10: 0073383090
ISBN 13: 978-0-07338-309-5

Chapter 1 - Section 1.3 - Propositional Equivalences - Exercises - Page 35: 14

Answer

$(\neg p\wedge(p\rightarrow q))\rightarrow\neg q$ is not a tautology

Work Step by Step

$\left[\begin{array}{ll} p & q\\ \hline & \\ T & T\\ T & F\\ F & T\\ F & F \end{array}\right. \left|\begin{array}{lll} \neg p & p\rightarrow q & \neg p\wedge(p\rightarrow q)\\ \hline & & \\ F & T & F\\ F & F & F\\ T & T & T\\ T & T & T \end{array}\right|\left.\begin{array}{ccc} \neg q & (\neg p\wedge(p\rightarrow q))\rightarrow\neg q\\ \hline & \\ F & T\\ T & T\\ F & F\\ T & T \end{array}\right]$ $(\neg p\wedge(p\rightarrow q))\rightarrow\neg q $ does not have all T values in its column, so it is not a tautology. (in row 3, $T\rightarrow F$ is false)
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