Homework 13

Read: Sections 3.2 and 3.3.

Turn in: 3.21(a), 3.23, 3.28, 3.30, 3.31

• Please read all Theorem 3.21 and also Theorem 3.22. They are important tools for working with sets.
• Section 3.2 provides for some fun reading and raises important foundational questions (but addressing them properly is done in a different class: Math 162). Here’s a reformulation of Problem 3.26: if $U$ is the collection of all sets and $S = \{A\in U\mid A\notin A\}$, then which is true: $S\in S$ or $S\notin S$?
• When working on 3.30, don’t forget that you can use previous results (like Theorem 3.10).

Extra practice: 3.22, 3.24–3.26