Set

A set is an unordered collection of unique elements.

Let $A=\{x_1,x_2,x_3,x_4\},B=x_4,x_5,x_6$

About

Order doesn’t matter $\{x_1,x_2,x_3\}=\{x_3,x_2,x_1\}$

Set membership

$x_1\in B=true{x}_1\notin B=false$

Related

• Subset
• Power Set