Product Inverse in Ring is Unique
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Theorem
Let $\struct {R, +, \circ}$ be a ring with unity.
Let $x \in R$ be a unit of $R$.
Then the product inverse $x^{-1}$ of $x$ is unique.
Proof
By definition of ring with unity, the algebraic structure $\struct {R, \circ}$ is a monoid.
The result follows from Inverse in Monoid is Unique.
$\blacksquare$
Sources
- 1969: C.R.J. Clapham: Introduction to Abstract Algebra ... (previous) ... (next): Chapter $4$: Fields: $\S 14$. Definition of a Field