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: 22

Answer

No such book can exist. Attempting to construct one leads to a logical contradiction due to self-reference. This is a paradox of **self-inclusion** — and shows the limits of naive self-reference in formal systems.

Work Step by Step

### Problem: **Can there exist a book that refers to all those books and only those books that do not refer to themselves?** --- ### ✅ Short Answer: \[ \boxed{\text{No, such a book cannot exist.}} \] --- ### 🧠 Explanation: This is a **version of Russell’s Paradox**. Let’s suppose such a book **B** exists. Book **B** contains a list of **all books that do not refer to themselves**. Now ask the key question: > **Does book B refer to itself?** --- ### ❗ Case 1: B **does** refer to itself. Then B refers to a book that refers to itself → which it’s **not supposed to list**. **Contradiction.** --- ### ❗ Case 2: B **does not** refer to itself. Then B satisfies the condition of books that **do not** refer to themselves → so it **should be in its own list**. But that would mean it **does** refer to itself. **Contradiction again.** --- ### 🔁 This loop is exactly the structure of **Russell's Paradox**: > Let R be the set of all sets that do not contain themselves. > Does R contain itself?
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