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[Pranav <>]

I want to understand difference between Manifolds and quasi-manifolds.
Quoting a para in  section
<http://doc.cgal.org/latest/Combinatorial_map/index.html> *2.4 Combinatorial
Map Properties* 

"...In 2D, quasi-manifolds are manifolds, but this is no longer true in
higher dimension as we can see in the example presented in Figure 24.6. In
this example, the object to the right is not a manifold since the
neighborhood of the point p in the object is not homeomorphic to a 3D ball
(intuitively, two objects are homeomorphic if each object can be
continuously deformed into the second one; in such a case, the two objects
have exactly the same topological properties)..."

Can anyone explain what does it mean(geometrically) to say : *"...the
neighborhood of the point p in the object is not homeomorphic to a 3D
ball..."*?

Is 3D-ball same as  3-sphere <http://en.wikipedia.org/wiki/3-sphere>  ?

The term /quasi-manifold/ seems specific to CGAL as I do not find it
anywhere else(atleast on simple googling).



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