# Prime element

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A generalization of the notion of a prime number. Let be an integral domain or commutative semi-group with an identity. A non-zero element that is not a divisor of unity is called prime if a product can be divided by only if one of the elements or can be divided by . Every prime element is irreducible, i.e. is divisible only by divisors of unity or elements associated to it. An irreducible element need not be prime; however, in a Gauss semi-group both concepts coincide. Moreover, if every irreducible element of a semi-group is prime, then is a Gauss semi-group. Analogous statements hold for a factorial ring. An element of a ring is prime if and only if the principal ideal generated by this element is a prime ideal.

There are generalizations of these notions to the non-commutative case (cf. [2]).

#### References

 [1] P.M. Cohn, "Free rings and their relations" , Acad. Press (1971) [2] A.G. Kurosh, "Lectures on general algebra" , Chelsea (1963) (Translated from Russian) [3] S. Lang, "Algebra" , Addison-Wesley (1974)