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