Lemma 27.11.4. With hypotheses and notation as in Lemma 27.11.1 above. Assume $A_ d \to B_ d$ is an isomorphism for all $d \gg 0$. Then

$U(\psi ) = Y$,

$r_\psi : Y \to X$ is an isomorphism, and

the maps $\theta : r_\psi ^*\mathcal{O}_ X(n) \to \mathcal{O}_ Y(n)$ are isomorphisms.

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