Definition:Inverse of Subset/Group
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Definition
Let $\struct {G, \circ}$ be a group.
Let $X \subseteq G$.
Then the inverse of the subset $X$ is defined as:
- $X^{-1} = \set {x \in G: x^{-1} \in X}$
or equivalently:
- $X^{-1} = \set {x^{-1}: x \in X}$
Examples
Subset of $\R$ under Multiplication
Let $\struct {\R, \times}$ be the multiplicative group of (non-zero) real numbers.
Let $S = \set {-1, 2}$.
Then the inverse $S^{-1}$ of $S$ is:
- $S^{-1} = \set {-1, \dfrac 1 2}$
Sources
- 1967: George McCarty: Topology: An Introduction with Application to Topological Groups ... (previous) ... (next): Chapter $\text{II}$: Groups: Subgroups
- 1978: Thomas A. Whitelaw: An Introduction to Abstract Algebra ... (previous) ... (next): Chapter $7$: Cosets and Lagrange's Theorem: Exercise $6$
- 1982: P.M. Cohn: Algebra Volume 1 (2nd ed.) ... (previous) ... (next): $\S 3.2$: Groups; the axioms