Eells–Kuiper Manifold
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In mathematics, an Eells–Kuiper manifold is a compactification of \R^n by a
sphere A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...
of dimension n/2, where n=2,4,8, or 16. It is named after
James Eells James Eells (October 25, 1926 – February 14, 2007) was an American mathematician, who specialized in mathematical analysis. Biography Eells was born on 25 October 1926, in Cleveland, Ohio. Eells studied mathematics at Bowdoin College in Ma ...
and
Nicolaas Kuiper Nicolaas Hendrik Kuiper (; 28 June 1920 – 12 December 1994) was a Dutch mathematician, known for Kuiper's test and proving Kuiper's theorem. He also contributed to the Nash embedding theorem. Kuiper studied at University of Leiden in 1937- ...
. If n=2, the Eells–Kuiper manifold is
diffeomorphic In mathematics, a diffeomorphism is an isomorphism of differentiable manifolds. It is an invertible function that maps one differentiable manifold to another such that both the function and its inverse are continuously differentiable. Defini ...
to the
real projective plane 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. It is the sett ...
\mathbb^2. For n\ge 4 it is
simply-connected In topology, a topological space is called simply connected (or 1-connected, or 1-simply connected) if it is path-connected and every path between two points can be continuously transformed into any other such path while preserving the two endpoint ...
and has the integral cohomology structure of the
complex projective plane In mathematics, the complex projective plane, usually denoted or is the two-dimensional complex projective space. It is a complex manifold of complex dimension 2, described by three complex coordinates :(Z_1,Z_2,Z_3) \in \C^3, \qquad (Z_1,Z_2, ...
\mathbb^2 (n = 4), of the quaternionic projective plane \mathbb^2 (n = 8) or of the
Cayley projective plane In mathematics, the Cayley plane (or octonionic projective plane) P2(O) is a projective plane over the octonions.Baez (2002). The Cayley plane was discovered in 1933 by Ruth Moufang, and is named after Arthur Cayley for his 1845 paper describing ...
(n = 16).


Properties

These manifolds are important in both
Morse theory In mathematics, specifically in differential topology, Morse theory enables one to analyze the topology of a manifold by studying differentiable functions on that manifold. According to the basic insights of Marston Morse, a typical differenti ...
and foliation theory: Theorem: ''Let M be a
connected Connected may refer to: Film and television * ''Connected'' (2008 film), a Hong Kong remake of the American movie ''Cellular'' * '' Connected: An Autoblogography About Love, Death & Technology'', a 2011 documentary film * ''Connected'' (2015 TV ...
closed
manifold In mathematics, a manifold is a topological space that locally resembles Euclidean space near each point. More precisely, an n-dimensional manifold, or ''n-manifold'' for short, is a topological space with the property that each point has a N ...
(not necessarily
orientable In mathematics, orientability is a property of some topological spaces such as real vector spaces, Euclidean spaces, surfaces, and more generally manifolds that allows a consistent definition of "clockwise" and "anticlockwise". A space is o ...
) of dimension n. Suppose M admits a
Morse function In mathematics, specifically in differential topology, Morse theory enables one to analyze the topology of a manifold by studying differentiable functions on that manifold. According to the basic insights of Marston Morse, a typical differenti ...
f\colon M\to \R of class C^3 with exactly three singular points. Then M is a Eells–Kuiper manifold.'' Theorem:. ''Let M^n be a compact connected manifold and F a Morse foliation on M. Suppose the number of centers c of the foliation F is more than the number of
saddle A saddle is a supportive structure for a rider of an animal, fastened to an animal's back by a girth. The most common type is equestrian. However, specialized saddles have been created for oxen, camels and other animals. It is not know ...
s s. Then there are two possibilities:'' * ''c=s+2, and M^n is homeomorphic to the sphere S^n'', * ''c=s+1, and M^n is an Eells–Kuiper manifold, n=2,4,8 or 16.''


See also

* Reeb sphere theorem


References

Foliations Manifolds {{topology-stub