In mathematics and logic, the phrase “there is one and only one” is used to indicate that exactly one object with a certain property exists. In mathematical logic, this sort of quantification is known as uniqueness quantification or unique existential quantification. Uniqueness quantification is often denoted with the symbols “∃!” or ∃=1″. For example, the formal statement may be read aloud as “there is exactly one natural number n such that n – 2 = 4”.