Example 38.37.11. Let $A$ be a ring. Let $f_1, f_2 \in A$ be elements.

\[ \xymatrix{ E = \text{Proj}(A/(f_1, f_2)[T_0, T_1]) \ar[r] \ar[d] & \text{Proj}(A[T_0, T_1]/(f_2 T_0 - f_1 T_1) = X' \ar[d] \\ Z = \mathop{\mathrm{Spec}}(A/(f_1, f_2)) \ar[r] & \mathop{\mathrm{Spec}}(A) = X } \]

is an almost blowup square.

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