linguistic:paraphrasing, quality:corruption, information:extraction
Definition

Let f {\displaystyle f} be a function whose domain is a set X. {\displaystyle X.} The function f {\displaystyle f} is said to be injective provided that for all a {\displaystyle a} and b {\displaystyle b} in X, {\displaystyle X,} if f (a) = f (b), {\displaystyle f(a)=f(b),} then a = b {\displaystyle a=b}; that is, f (a) = f (b) {\displaystyle f(a)=f(b)} implies a = b. {\displaystyle a=b.} Equivalently, if a ≠ b, {\displaystyle a\neq b,} then f (a) ≠ f (b) {\displaystyle f(a)\neq f(b)} in the contrapositive statement.

Symbolically,

which is logically equivalent to the contrapositive,