# Prime ring

In abstract algebra, a nonzero ring R is a prime ring if for any two elements a and b of R, arb = 0 for all r in R implies that either a = 0 or b = 0. This definition can be regarded as a simultaneous generalization of both integral domains and simple rings.

Although this article discusses the above definition, prime ring may also refer to the minimal non-zero subring of a field, which is generated by its identity element 1, and determined by its characteristic. For a characteristic 0 field, the prime ring is the integers, for a characteristic p field (with p a prime number) the prime ring is the finite field of order p (cf. prime field).

## Equivalent definitions

A ring R is prime if and only if the zero ideal {0} is a prime ideal in the noncommutative sense.

This being the case, the equivalent conditions for prime ideals yield the following equivalent conditions for R to be a prime ring:

• For any two ideals A and B of R, AB = {0} implies A = {0} or B = {0}.
• For any two right ideals A and B of R, AB = {0} implies A = {0} or B = {0}.
• For any two left ideals A and B of R, AB = {0} implies A = {0} or B = {0}.

Using these conditions it can be checked that the following are equivalent to R being a prime ring:

• All nonzero right ideals are faithful as right R modules.
• All nonzero left ideals are faithful as left R modules.

## Examples

• Any domain is a prime ring.
• Any simple ring is a prime ring, and more generally: every left or right primitive ring is a prime ring.
• Any matrix ring over an integral domain is a prime ring. In particular, the ring of 2-by-2 integer matrices is a prime ring.

## Properties

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