A set N together with two binary operations + (called addition) and ⋅ (called multiplication) is called a (right) near-ring if:
A1: N is a group (not necessarily abelian) under addition;
A2: multiplication is associative (so N is a semigroup under multiplication); and
A3: multiplication distributes over addition on the right: for any x, y, z in N, it holds that (x + y)⋅z = (x⋅z) + (y⋅z).[1]
Similarly, it is possible to define a left near-ring by replacing the right distributive law A3 by the corresponding left distributive law. However, near-rings are almost always written as right near-rings.[citation needed]
An immediate consequence of this one-sided distributive law is that it is true that 0⋅x = 0 but it is not necessarily true that x⋅0 = 0 for any x in N. Another immediate consequence is that (−x)⋅y = −(x⋅y) for any x, y in N, but it is not necessary that x⋅(−y) = −(x⋅y). A near-ring is a ring (not necessarily with unity) if and only if addition is commutative and multiplication is distributive over addition on the left.