The unique existential quantifer is the symbol ∃!. For example,
means "there exists an unique x such that x-2 = 4".
History of the Quantifer
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See Existential quantification for details.
... choreographer (+ 1983) January 26 - Ancel Keys, scientist February 1 - S. J. Perelman[?], humorist, author February 4 - MacKinlay Kantor[?], historian (+ 1977) ...