Near-rings

Abbreviation: NRng

Definition

A near-ring is a structure $\mathbf{N}=\langle N,+,-,0,\cdot \rangle$ of type $\langle 2,1,0,2\rangle$ such that

$\langle N,+,-,0\rangle$ is a groups

$\langle N,\cdot \rangle$ is a semigroups

$\cdot$ right-distributes over $+$: $(x+y)\cdot z=x\cdot z+y\cdot z$

Morphisms

Let $\mathbf{M}$ and $\mathbf{N}$ be near-rings. A morphism from $\mathbf{M}$ to $\mathbf{N}$ is a function $h:M\rightarrow N$ that is a homomorphism:

$h(x+y)=h(x)+h(y)$, $h(x\cdot y)=h(x)\cdot h(y)$

Remark: It follows that $h(0)=0$ and $h(-x)=-h(x)$.

Examples

Example 1: $\langle\mathbb{R}^{\mathbb{R}},+,-,0,\cdot\rangle$, the near-ring of functions on the real numbers with pointwise addition, subtraction, zero, and composition.

Basic results

$0$ is a zero for $\cdot$: $0\cdot x=0$ and $x\cdot 0=0$.

Properties

Classtype variety decidable no unbounded no yes yes, $n=2$ yes yes

Finite members

$\begin{array}{lr} f(1)= &1\\ f(2)= &\\ f(3)= &\\ f(4)= &\\ f(5)= &\\ f(6)= &\\ \end{array}$