The Stacks project

Lemma 27.11.2. Let $A$, $B$, and $C$ be graded rings. Set $X = \text{Proj}(A)$, $Y = \text{Proj}(B)$ and $Z = \text{Proj}(C)$. Let $\varphi : A \to B$, $\psi : B \to C$ be graded ring maps. Then we have

\[ U(\psi \circ \varphi ) = r_\psi ^{-1}(U(\varphi )) \quad \text{and} \quad r_{\psi \circ \varphi } = r_\varphi \circ r_\psi |_{U(\psi \circ \varphi )}. \]

In addition we have

\[ \theta _\psi \circ r_\psi ^*\theta _\varphi = \theta _{\psi \circ \varphi } \]

with obvious notation.

Proof. Omitted. $\square$


Comments (2)

Comment #8511 by Jordan on

Shouldn't it be ? I'd expect to obtain by first forming the open in , and then pulling it back to to form .

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  • 2 comment(s) on Section 27.11: Functoriality of Proj

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