Injective Function - Definition

Definition

Let f be a function whose domain is a set A. The function f is injective if for all a and b in A, if f(a) = f(b), then a = b; that is, f(a) = f(b) implies a = b. Equivalently, if ab, then f(a) ≠ f(b).

Symbolically,

which is logically equivalent to the contrapositive,

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