- #1

- 49

- 3

I got confused at what this [itex]B= \{x \in A : x \not\in f(x) \} [/itex] is and

how it's true that [itex]If~y \in A ~\text{is such that}~f(y)=B, \text{where is y? It must be either in}~B~\text{or in} A \setminus B.[/itex]

Can anyone explain what's going on here?