Refers to a one-to-one correspondence between the objects in two sets.
Example
The rule \(f : \textrm{A} \rightarrow \textrm{B} : x \mapsto 2^x\) is a one-to-one relation.
The rule \(f : \textrm{A} \rightarrow \textrm{B} : x \mapsto 2^x\) is a one-to-one relation.