Definition:Antihomomorphism
Definition
Let $\phi: \struct {S, \circ} \to \struct {T, *}$ be a mapping from one algebraic structure $\struct {S, \circ}$ to another $\struct {T, *}$.
Then $\phi$ is an antihomomorphism if and only if:
- $\forall x, y \in S: \map \phi {x \circ y} = \map \phi y * \map \phi x$
For structures with more than one operation, $\phi$ may be antihomomorphic for a subset of those operations.
Group Antihomomorphism
Let $\struct {S, \circ}$ and $\struct {T, *}$ be groups.
Then $\phi: S \to T$ is a group antihomomorphism if and only if:
- $\forall x, y \in S:\map \phi {x \circ y} = \map \phi y * \map \phi x$
Ring Antihomomorphism
Let $\struct {R, +, \circ}$ and $\struct {S, \oplus, *}$ be rings.
Then $\phi: R \to S$ is a ring antihomomorphism if and only if:
\(\ds \forall a, b \in R: \, \) | \(\ds \map \phi {a + b}\) | \(=\) | \(\ds \map \phi a \oplus \map \phi b\) | |||||||||||
\(\ds \forall a, b \in R: \, \) | \(\ds \map \phi {a \circ b}\) | \(=\) | \(\ds \map \phi b * \map \phi a\) |
Field Antihomomorphism
Let $\struct {R, +, \circ}$ and $\struct {S, \oplus, *}$ be fields.
Then a ring antihomomorphism $\phi: \struct {R, +, \circ} \to \struct {S, \oplus, *}$ is called a field antihomomorphism.