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[parent] nil is a radical property (Proof)

We must show that the nil property, $ \mathcal{N}$, is a radical property, that is that it satisfies the following conditions:

  1. The class of $ \mathcal{N}$-rings is closed under homomorphic images.
  2. Every ring $ R$ has a largest $ \mathcal{N}$-ideal, which contains all other $ \mathcal{N}$-ideals of $ R$. This ideal is written $ \mathcal{N}(R)$.
  3. $ \mathcal{N}(R/\mathcal{N}(R)) = 0$.

It is easy to see that the homomorphic image of a nil ring is nil, for if $ f \colon R \to S$ is a homomorphism and $ x^n = 0$, then $ f(x)^n = f(x^n) = 0$.

The sum of all nil ideals is nil (see proof here), so this sum is the largest nil ideal in the ring.

Finally, if $ N$ is the largest nil ideal in $ R$, and $ I$ is an ideal of $ R$ containing $ N$ such that $ I/N$ is nil, then $ I$ is also nil (see proof here). So $ I \subseteq N$ by definition of $ N$. Thus $ R/N$ contains no nil ideals.



"nil is a radical property" is owned by mclase.
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See Also: properties of nil and nilpotent ideals


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Cross-references: proof, nil ideals, sum, homomorphism, nil ring, easy to see, ideal, contains, ring, homomorphic images, closed under, class, radical property, property, nil
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This is version 2 of nil is a radical property, born on 2004-02-28, modified 2004-02-28.
Object id is 5651, canonical name is NilIsARadicalProperty.
Accessed 2007 times total.

Classification:
AMS MSC16N40 (Associative rings and algebras :: Radicals and radical properties of rings :: Nil and nilpotent radicals, sets, ideals, rings)

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