Lemma 51.4.5. Let A \to B be a ring map. Let I \subset A be a finitely generated ideal. Then \text{cd}(B, IB) \leq \text{cd}(A, I). If A \to B is faithfully flat, then equality holds.
Proof. Use the definition and Dualizing Complexes, Lemma 47.9.3. \square
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