Section 3.2

Section 3.2 covers Russell's paradox. Note that in pure set theory, the paradox is produced by considering the set $\{x:x\notin x\}$; this is what you will find if you look up the paradox in places like Wikipedia. However, in this book Tao distinguishes between sets and other types of objects such as numbers. This is why he uses the slightly more complicated property that requires $x$ to be a set.