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| | Math 423, Fall, 2002 (Site not responding. Last check: 2007-09-20) |
 | | The first is that manifolds, and also more general spaces, can be thought of as being constructed from building-blocks called simplices, points, line segments, triangles, tetrahedra, etc. It is true that any compact manifold is homeomorphic to a union of such objects, in a very specific way. |
 | | If it is possible to do so, then the manifold M is orientable, and an orientation is a choice of such local coordinates, compatible with each other at each point. |
 | | If a manifold is not orientable, all is not lost (though the upcoming definition of integration over M will be). |
| www.lehigh.edu /~dlj0/courses/423f02-lect20.html (2384 words) |
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