How can membership in a set be shown with the symbols ∈ and ∉?

In set theory, the symbols $\in$ and $\notin$ are used to denote membership within a collection of objects.12

• Membership ($\in$): To indicate that a specific object $x$ is a member of a set $A$, you write $x\in A$.12
• Non-membership ($\notin$): To indicate that an object $x$ is not a member of a set $A$, you write $x\notin A$. This is formally understood as the negation of the membership relation, often abbreviated from the expression $~(x\in A)$.12

These symbols are fundamental to the logic of classes, where a set can be defined either by listing its members or by specifying a condition that its members must satisfy.12