\begin{definition}[Definition:Existential Quantifier/Unique/Also denoted as]
The symbol $\exists_1$ is also found for the same concept, being an instance of the exact existential quantifier $\exists_n$.
Some sources, for example {{BookReference|Axiomatic Set Theory|1972|Patrick Suppes}}, use $\operatorname E !$, which is idiosyncratic, considering the use in the same source of $\exists$ for the general existential quantifier.
\end{definition}