ScalingStacks

Example 7.2 . [02ZT]

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Example 7.2.

Take ๐’ณ\mathcal{X} to be defined by the equation tโ€‹f4+z0โ€‹z1โ€‹z2โ€‹z3=0tf_{4}+z_{0}z_{1}z_{2}z_{3}=0 in โ„™3ร—D\mathbb{P}^{3}\times D, where DD is a disk with coordinate tt and f4f_{4} is a general homogeneous quartic polynomial on โ„™3\mathbb{P}^{3}. It is easy to see that ๐’ณ\mathcal{X} is singular at the locus

{t=f4=0}โˆฉSing(๐’ณ0).\{t=f_{4}=0\}\cap Sing(\mathcal{X}_{0}).

As ๐’ณ0\mathcal{X}_{0} is the coordinate tetrahedron, the singular locus of ๐’ณ0\mathcal{X}_{0} consists of the six coordinate lines of โ„™3\mathbb{P}^{3}, and ๐’ณ\mathcal{X} has four singular points along each such line, for a total of 24 singular points. Take Z=Sโ€‹iโ€‹nโ€‹gโ€‹(๐’ณ)Z=Sing(\mathcal{X}). Then away from ZZ, the projection ๐’ณโ†’D\mathcal{X}\rightarrow D is normal crossings, which yields condition (4) of the definition of toric degeneration. It is easy to see all other conditions are satisfied.

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