stationary duality, Spanier duality
A duality in homotopy theory which exists (in the absence of restrictions imposed on the dimensions of spaces) for the analogues of ordinary homotopy and cohomotopy groups in the suspension category — for the -homotopy and -cohomotopy groups or stationary homotopy and cohomotopy groups, forming extra-ordinary (generalized) homology and cohomology theories. A suspension category, or -category, is a category whose objects are topological spaces , while its morphisms are classes of -homotopic mappings from a -fold suspension into , and being considered as -homotopic if there exists an such that the suspensions and are homotopic in the ordinary sense. The set of such classes, which are known as -mappings, constitutes an Abelian group with respect to the so-called track addition , , , . The group is the limit of the direct spectrum of the sets of ordinary homotopy classes with suspension mappings as projections; if is sufficiently large, it is a group spectrum with homomorphisms. There exists an isomorphism in which the corresponding elements are represented by one and the same mapping , . The -dual polyhedron of the polyhedron in a sphere is an arbitrary polyhedron in which is an -deformation retract of the complement , i.e. the morphism corresponding to the imbedding is an -equivalence. The polyhedron exists for all , and may be considered as .
For any polyhedra and any polyhedra and which are dual to them, there exists a unique mapping
satisfying the following conditions:
a) It is an involutory contravariant functorial isomorphism, i.e. is a homomorphism such that if
if is an element of or of , then .
b) The following relations are valid:
where and are considered as polyhedra, -dual to polyhedra and, correspondingly, , this means that it does not depend on and is stationary with respect to suspension.
c) It satisfies the equation
are homomorphisms of the above homology and cohomology groups, induced by -mappings and , and
is an isomorphism obtained from the isomorphism of Alexander duality by replacing the set by its -deformation retract .
The construction of is based on the representation of a given mapping as the composition of an imbedding and an -deformation retract.
The -homotopy group of a space is the group , and the -cohomotopy group of is the group . As in ordinary homotopy theory, one defines the homomorphisms
Regarding the spheres and as -dual leads to the isomorphisms
and to the commutative diagram
Thus, the isomorphism connects -homotopy and -cohomotopy groups, just as the isomorphism of Alexander duality connects the homology and cohomology groups. Any duality in the -category entails a duality of ordinary homotopy classes if the conditions imposed on the space entail the existence of a one-to-one correspondence between the set of the above classes and the set of -homotopy classes.
Examples of dual assumptions in this theory include Hurewicz's isomorphism theorem and Hopf's classification theorem. converts one of these theorems into the other, which means that -homotopy groups are replaced by -cohomotopy groups, homology groups by cohomology groups, the mapping by the mapping , the smallest dimension with a non-trivial homology group by the largest dimension with a non-trivial cohomology group, and vice versa. In ordinary homotopy theory the definition of an -cohomotopy group requires that the dimension of the space does not exceed (or, more generally, that the space be -coconnected, ), which impairs the perfectly general nature of duality.
There are several trends of generalization of the theory: e.g. studies are made of spaces with the -homotopy type of polyhedra, the relative case, a theory with supports, etc. , , , . The theory was one of the starting points in the development of stationary homotopy theory .
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S-duality. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=S-duality&oldid=23971