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Cusps, triangle groups and hyperbolic 3-folds
... definitions and properties of these groups. We say an orbifold Q is cusped if it is noncompact and of finite volume. The singular set of Q is the set of non-manifold points, that is, the projection to the orbit space of the set of fixed points of elements of F\{identity}. The degree of a point in th ...
... definitions and properties of these groups. We say an orbifold Q is cusped if it is noncompact and of finite volume. The singular set of Q is the set of non-manifold points, that is, the projection to the orbit space of the set of fixed points of elements of F\{identity}. The degree of a point in th ...
Perfectly Normal Non-metrizable Non
... Definition. X is called a K0 space if it has a σ-discrete dense subspace. Clearly, σ-dcc is a generalization of ccc, and both K0 and K0 are generalizations of separable. Surprisingly, there is an example of a LOTS which is K0 (in fact metrizable) but has an antichain of open sets which is not σ-di ...
... Definition. X is called a K0 space if it has a σ-discrete dense subspace. Clearly, σ-dcc is a generalization of ccc, and both K0 and K0 are generalizations of separable. Surprisingly, there is an example of a LOTS which is K0 (in fact metrizable) but has an antichain of open sets which is not σ-di ...
3-manifold
![](https://commons.wikimedia.org/wiki/Special:FilePath/3-Manifold_3-Torus.png?width=300)
In mathematics, a 3-manifold is a space that locally looks like Euclidean 3-dimensional space. Intuitively, a 3-manifold can be thought of as a possible shape of the universe. Just like a sphere looks like a plane to a small enough observer, all 3-manifolds look like our universe does to a small enough observer. This is made more precise in the definition below.