The complete-intersection semigroup-condition conjecture for splice diagrams

Let XX be a surface singularity with homology sphere link, and let Δ\Delta be its splice diagram. For each node vv and adjacent edge ee, the semigroup condition requires the edge weight dved_{ve} to lie in the semigroup generated by the relevant linking numbers:

dveNvw:w a leaf of Δ in Δve.d_{ve}\in\mathbb{N}\langle\ell'_{vw}:w\text{ a leaf of }\Delta\text{ in }\Delta_{ve}\rangle.

Complete-intersection semigroup-condition conjecture. If XX is a complete intersection, then Δ\Delta satisfies the semigroup condition.

If true, this would make the combinatorial semigroup condition necessary as well as sufficient for constructing complete intersection singularities of splice type with prescribed homology-sphere links. The paper reports no counterexample.

Sources & referencesView supporting material

Primary source

Walter D. Neumann and Jonathan Wahl, “Complex surface singularities with integral homology sphere links”, arXiv:math/0301165 (2005).

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