Galois correspondence of extension and contraction

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Statement

Suppose f:RS is a homomorphism of commutative unital rings. Then, let Ideals(R) and Ideals(S) denote the set of ideals in R and S respectively, viewed as partially ordered sets by inclusion. Consider the following maps:

  • The extension map which sends an ideal of R to the ideal generated by its image in S:

_e:Ideals(R)Ideals(S)

  • The contraction map which sends an ideal of S to its full inverse image in R:

_c:Ideals(S)Ideals(R)