ThmDex – An index of mathematical definitions, results, and conjectures.

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▼	Set of symbols
▼	Propositional connective
▼	Set of propositional connectives
▼	Complete set of propositional connectives
▼	Set of propositional symbols
▼	Set of predicate symbols
▼	Set-theoretic alphabet
▼	Set-theoretic language
▼	Set-theoretic expression
▼	Set-theoretic formula
▼	Class term
▼	Empty set

Definition D2115

Nonempty set

Formulation 0

Let

$\emptyset$ be the D13: Empty set.
A D11: Set

$x$ is non-empty if and only if

$\begin{equation} x \neq \emptyset \end{equation}$