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A generator for the fundamental group is the closed curve obtained by projecting any curve connecting antipodal points in down to . The projective n {\displaystyle n} -space is compact, connected, and has a fundamental group isomorphic to the cyclic group of order 2: its universal covering space is given by the antipody ...
Homology groups are finitely generated abelian groups, and homology classes are elements of these groups. The Betti numbers of the manifold are the rank of the free part of the homology group, and in the special case of surfaces, the torsion part of the homology group only occurs for non-orientable cycles.
Since C −1 = 0, every 0-chain is a cycle (i.e. Z 0 = C 0); moreover, the group B 0 of the 0-boundaries is generated by the three elements on the right of these equations, creating a two-dimensional subgroup of C 0. So the 0th homology group H 0 (S) = Z 0 /B 0 is isomorphic to Z, with a basis given (for example) by the image of the 0-cycle (v 0).
In mathematics, the real projective plane, denoted or , is a two-dimensional projective space, similar to the familiar Euclidean plane in many respects but without the concepts of distance, circles, angle measure, or parallelism.
Let X be a topological space and A, B be two subspaces whose interiors cover X. (The interiors of A and B need not be disjoint.) The Mayer–Vietoris sequence in singular homology for the triad (X, A, B) is a long exact sequence relating the singular homology groups (with coefficient group the integers Z) of the spaces X, A, B, and the intersection A∩B. [8]
The first homology group is now defined as the quotient group: ():= / Here, is the group of 1-dimensional cycles, which is isomorphic to Z 2, and is the group of 1-dimensional cycles that are boundaries of 2-dimensional cells, which is isomorphic to Z.
In homological algebra, the mapping cone is a construction on a map of chain complexes inspired by the analogous construction in topology.In the theory of triangulated categories it is a kind of combined kernel and cokernel: if the chain complexes take their terms in an abelian category, so that we can talk about cohomology, then the cone of a map f being acyclic means that the map is a quasi ...
In mathematics, the Poincaré duality theorem, named after Henri Poincaré, is a basic result on the structure of the homology and cohomology groups of manifolds.It states that if M is an n-dimensional oriented closed manifold (compact and without boundary), then the kth cohomology group of M is isomorphic to the (n − k) th homology group of M, for all integers k