Lemma 10.122.8. Let R \to S be a ring map of finite type. Let R \to R' be any ring map. Set S' = R' \otimes _ R S.
The set \{ \mathfrak q' \mid R' \to S' \text{ quasi-finite at }\mathfrak q'\} is the inverse image of the corresponding set of \mathop{\mathrm{Spec}}(S) under the canonical map \mathop{\mathrm{Spec}}(S') \to \mathop{\mathrm{Spec}}(S).
If \mathop{\mathrm{Spec}}(R') \to \mathop{\mathrm{Spec}}(R) is surjective, then R \to S is quasi-finite if and only if R' \to S' is quasi-finite.
Any base change of a quasi-finite ring map is quasi-finite.
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