4. Reconstruction of the complex hypersurface from a balanced polyhedron Π [04SW]
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4. Reconstruction of the complex hypersurface from a balanced polyhedron
Theorem 1’ can be treated as a pair-of-pants decomposition for . We can use this presentation to reconstruct from . This allows to interpret a maximal balanced polyhedral complex as the complex encoding the gluing pattern of pairs-of-pants in order to get . Here is the way to reconstruct from .
For each vertex of take a copy of . This copy can be identified with the localized hyperplane . Recall that by Proposition 1.24 consists of components. Each such component corresponds to a 1-cell of adjacent to .
Let be a 1-cell of connecting the vertices and . For each such 1-cell we identify the closures and of the corresponding components of and in the following way.
Without the loss of generality we may assume that in both copies of the edge corresponds to the facet of (see 3.4). (Note that such correspondence is given by matrices from Proposition 1.11.) We attach to by the map
where is the complex conjugate to .
The result of this gluing is a manifold with boundary. The boundary comes from the unbounded cells of . Denote . The boundary is formed by the closures of the components of that correspond to unbounded 1-cells in . By Proposition 1.24 each such is a circle fibration over a union of lower-dimensional pairs-of-pants . Let be the result of collapsing all fibers of these fibrations on . Note that is canonically a smooth manifold since this procedure locally coincides with collapsing the boundary on which results in .
Theorem 4.
The manifold is diffeomorphic to . The manifold is diffeomorphic to .
Corollary 4.1.
The manifolds and depend only on the lattice polygon associated to , not on itself.
Remark 4.2.
With a little more care this reconstruction process can be made in the symplectic category, i.e. the result of gluing can be given a natural symplectic structure. This is due to the following two reasons. The first one is that the pair-of-pants possesses a natural symplectic structure (the one which gives the standard symplectic after the symplectic reduction of the boundary). The second one is that two pairs-of-pants get identified along a part of their boundary which is a symplectically flat hypersurface, it has a neighborhood symplectically isomorphic to , where is an annulus. This product is consistent with the -fibration from Proposition 1.24.