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[parent] unity of subring (Theorem)
Theorem 1   Let $S$ be a proper subring of the ring $R$ If $S$ has a non-zero unity $u$ which is not unity of $R$ then $u$ is a zero divisor of $R$

Proof. Because $u$ is not unity of $R$ there exists an element $r$ of $R$ such that $ru \neq r$ Then we have $(ru)u = r(uu) = ru$ which implies that $0 = (ru)u-ru = (ru-r)\cdot u$ Since neither $ru-r$ , nor $u$ , is 0, the element $u$ , is a zero divisor in $R$




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See Also: unities of ring and subring, corner of a ring


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Cross-references: implies, proof, zero divisor, unity, non-zero unity, ring, subring

This is version 4 of unity of subring, born on 2004-11-18, modified 2006-03-05.
Object id is 6492, canonical name is UnityOfSubring.
Accessed 1473 times total.

Classification:
AMS MSC13-00 (Commutative rings and algebras :: General reference works )
 16-00 (Associative rings and algebras :: General reference works )
 20-00 (Group theory and generalizations :: General reference works )

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