New posts in Elementary Set Theory

Prove a bijection between $\mathbb{N}^2$ and $\mathbb{N}$.

Subset of a set of sets

Can I conclude that $x=f(x)$ from the assumption that $f(x)=f(f(x))$?

What is ${\cal P}(A ) \cap A$?

Difficulty in understanding significance of Grelling's Paradox.

Difficulty Understanding Rudin's Example 2.10(b)

A finite set of distinct positive numbers is special if each integer in the set divides the sum of all integers within the set.

What axiom of ZFC implies that "sets have no repeated elements"?

For a function $f: X \to Y$, if $Y-V$ is finite, when is $X - f^{-1}(V)$ finite?

Bijective map from a set to a subset of reals?