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ring homomorphism (Definition)

Let $R$ and $S$ be rings. A ring homomorphism is a function $f: R \longrightarrow S$ such that:

  • $f(a+b) = f(a)+f(b)$ for all $a,b \in R$
  • $f(a\cdot b) = f(a) \cdot f(b)$ for all $a,b \in R$

A ring isomorphism is a ring homomorphism which is a bijection. A ring monomorphism (respectively, ring epimorphism) is a ring homomorphism which is an injection (respectively, surjection).

When working in a context in which all rings have a multiplicative identity, one also requires that $f(1_R) = 1_S$ Ring homomorphisms which satisfy this property are called unital ring homomorphisms.




"ring homomorphism" is owned by djao.
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See Also: ring

Also defines:  unital, ring isomorphism, ring epimorphism, ring monomorphism, homomorphism, isomorphism, epimorphism, monomprhism

Attachments:
field homomorphism (Definition) by alozano
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Cross-references: property, multiplicative identity, surjection, injection, bijection, function, rings
There are 86 references to this entry.

This is version 7 of ring homomorphism, born on 2001-10-19, modified 2006-10-22.
Object id is 357, canonical name is RingHomomorphism.
Accessed 15984 times total.

Classification:
AMS MSC13B10 (Commutative rings and algebras :: Ring extensions and related topics :: Morphisms)
 16B99 (Associative rings and algebras :: General and miscellaneous :: Miscellaneous)

Pending Errata and Addenda
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Epimorphisms /= Surjections by theroberts on 2009-06-13 03:21:44
In the category of rings, epimorphisms are not equivalent to surjections as the article currently states. The inclusion map from the integers to the rationals is epi, but not surjective.
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f(1)=1 dangerous by AxelBoldt on 2003-11-19 18:04:40
The f(1)=1 requirement for unitary rings has the following consequence: it is possible that f:R->S and g:S->T are ring homomorphisms, yet gf:R->T is not. So rings together with ring homomorphisms do not form a category.

So maybe one should distinguish between a "homomorphism of rings" and a "homomorphism of unitary rings".
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