Example 3.11 (A variation) . [04IC]
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Example 3.11 (A variation).
In the previous example, was a graph with three edges meeting in one vertex. All three edges were straight lines. In the spirit of Example 3.9 we can perturb each edge of to a smooth curve starting at the vertex. Each straight edge of the previous example is contained in a -plane which is an integral plane of the distribution spanned by the vectors which are invariant with respect to the holonomy around that edge. For example, consider the edge of . Then is contained inside the half plane, , whose tangent vectors are invariant, where is the holonomy of with respect to . An analogous thing happens with the other two edges. The union of all three half planes gives . The new perturbed edges, , must be curves inside the half planes . More precisely, let be a function on which is the restriction of a smooth function defined on an open neighborhood of , such that . If we let be as in the previous example, define
Now charts on can be defined like in the previous example, but with these new definitions of and . It is clear that defines an affine manifold with singularities. Two different choices of functions define non-isomorphic integral affine manifolds with singularities, unless their graphs inside can be mapped one to the other via an integral affine map.