central idempotent
Let be a ring. An element is called a central idempotent if it is an idempotent and is in the center of .
It is well-known that if is an idempotent, then has the structure of a ring with unity, with being the unity. Thus, if is central, is a ring with unity .
It is easy to see that the operation of ring multiplication preserves central idempotency: if are central idempotents, so is . In addition, if has a multiplicative identity , then is also a central idempotent. Furthermore, we may characterize central idempotency in a ring with as follows:
Proposition 1.
An idempotent in a ring with is central iff , where .
Proof.
If is central, then clearly . Conversely, for any , we have . ∎
Another interesting fact about central idempotents in a ring with unity is the following:
Proposition 2.
The set of all central idempotents of a ring with has the structure of a Boolean ring.
Proof.
First, note that . Next, for , we define addition and multiplication on as follows:
As discussed above, and are well-defined (as is closed under these operations). In addition, for any , we have
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1.
is a commutative monoid, in which every element is an idempotent (with respect to ). This fact is clear.
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2.
is commutative, since .
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3.
is associative:
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4.
distributes over : we only need to show left distributivity (since is commutative by above):
This shows that is a Boolean ring. ∎
Title | central idempotent |
---|---|
Canonical name | CentralIdempotent |
Date of creation | 2013-03-22 19:13:07 |
Last modified on | 2013-03-22 19:13:07 |
Owner | CWoo (3771) |
Last modified by | CWoo (3771) |
Numerical id | 5 |
Author | CWoo (3771) |
Entry type | Definition |
Classification | msc 16U99 |
Classification | msc 20M99 |