3.2. The elliptic curve and the K3-surface [04SH]
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3.2. The elliptic curve and the K3-surface
Here we consider the well-known fibrations of the elliptic curve and the K3-surface.
Let be an elliptic curve, i.e. a Riemann surface of genus 1. Since is topologically a torus, there is a trivial -fibration .
Suppose that the elliptic curve is presented as a curve in a toric surface , where is the Newton polygon of a polynomial defining . By the genus formula (see [8]), contains a unique lattice point. By Proposition 1.10 a dual -complex is homotopy equivalent to a circle. It is easy to see that the fibration from Theorem 1’ coincides up to homotopy with the trivial -fibration .
Another famous fibration has the K3-surface as its total space. All its fibers, except for 24 of them are Lagrangian tori.
Suppose that the polygon has exactly one interior lattice point. Then, by Khovanskii’s formula [8], the zero locus of a generic polynomial with the Newton polygon is a K3-surface. A dual -complex is homotopy equivalent to a sphere by Proposition 1.10.
Again, the fibration can be deformed to a fibration like by so-called shelling of 11 1 A higher-dimensional version of such deformation will be the subject for a future paper..
In higher dimensions, if is a non-singular polyhedron with a unique interior lattice point, then the corresponding hypersurface is a smooth Calabi-Yau manifold. Singular torus fibrations were constructed by Zharkov [17]. Ruan [13] noted that such fibrations can be made Lagrangian.
Theorem 1’ constructs in this case a stratified torus fibration over a polyhedral complex homotopy equivalent to .