What does the exclamation mark do? - Mathematics Stack …
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WEBNov 10, 2011 · An exclamation mark can also be shorthand for "unique". For example, the statement. ∀y ∈ f(A), ∃!x ∈ A s.t. y = f(x) ∀ y ∈ f ( A), ∃! x ∈ A s.t. y = f ( x) would be read as "for all y y in the range of f f, there exits a unique x x in the domain such that y = f(x) y = f ( x) ". In other words, f f is one-to-one. Share.
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