Set Equivalence behaves like Equivalence Relation

Theorem
Set equivalence is an equivalence relation.

Proof
For two sets to be equivalent, there needs to exist a bijection between them.

In the following, let $\phi$, $\phi_1$ and $\phi_2$ be understood to be bijections.

Also see
The definition of a cardinal of a set as the equivalence class of that set under set equivalence.