Extension and Contraction of Ideals - Properties

Properties

Assuming f : AB is a unital ring homomorphism, is an ideal in A, is an ideal in B, then:

  • is prime in B is prime in A.
  • It is false, in general, that being prime (or maximal) in A implies that is prime (or maximal) in B. Many classic examples of this stem from algebraic number theory. For example, embedding . In, the element 2 factors as where (one can show) neither of are units in B. So is not prime in B (and therefore not maximal, as well). Indeed, shows that, and therefore .

On the other hand, if f is surjective and then:

  • and .
  • is a prime ideal in A is a prime ideal in B.
  • is a maximal ideal in A is a maximal ideal in B.

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