Inverse of One-to-One Relation is One-to-One
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Theorem
The inverse of a one-to-one relation is a one-to-one relation.
Proof
Let $\RR$ be a one-to-one relation.
Let $\RR^{-1}$ denote its inverse
By definition, $\RR$ is a relation which is both many-to-one and one-to-many.
From Inverse of Many-to-One Relation is One-to-Many:
- $\RR^{-1}$ is both one-to-many and many-to-one.
Hence the result by definition of one-to-one relation.
$\blacksquare$