equivalence class

for every $\text{[math]}$ where $\text{[math]}$ is a non-empty set and $\text{[math]}$ , an equivalence class of $\text{[math]}$ is the set:
$\text{[math]}$

$\text{[math]}$ since those are sets, unlike an ordered pair the order of the numbers in sets doesnt matter so $\text{[math]}$ , and so we get:
$\text{[math]}$

consider the sets from a previous example:
$\text{[math]}$ we get:
$\text{[math]}$