Discrete Mathematics with Applications 4th Edition

Published by Cengage Learning
ISBN 10: 0-49539-132-8
ISBN 13: 978-0-49539-132-6

Chapter 6 - Set Theory - Exercise Set 6.4 - Page 382: 18

Answer

No, it is not a statement. It is self-referential and logically paradoxical.

Work Step by Step

### Problem 18: **"This sentence is false and 1 + 1 = 2."** --- ### โœ… Determine if it is a **statement**: A **statement** is a sentence that is either **true** or **false**, but **not ambiguous** or self-contradictory. --- ### ๐Ÿ” Letโ€™s Analyze: Letโ€™s call the sentence **S**: > **S**: "S is false and 1 + 1 = 2" The second part, \(1 + 1 = 2\), is **true**. So the sentence becomes: \[ S \equiv \text{"S is false"} \land \text{true} \Rightarrow S \equiv \text{"S is false"} \] So again: \[ S \equiv \text{"S is false"} \] This is the **liar paradox** in disguise โ€” it leads to contradiction: - If \(S\) is **true**, then it claims it is **false** โ‡’ contradiction. - If \(S\) is **false**, then what it says is false, meaning โ€œS is falseโ€ is false โ‡’ S is **true** โ‡’ contradiction. --- ### โŒ Conclusion: This self-referential sentence causes a paradox. It does **not** have a definite truth value, and therefore is **not a statement** in formal logic.
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