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Homotopy Fiber
In mathematics, especially homotopy theory, the homotopy fiber (sometimes called the mapping fiber)Joseph J. Rotman, ''An Introduction to Algebraic Topology'' (1988) Springer-Verlag ''(See Chapter 11 for construction.)'' is part of a construction that associates a fibration to an arbitrary continuous function of topological spaces f:A \to B. It acts as a homotopy theoretic kernel of a mapping of topological spaces due to the fact it yields a long exact sequence of homotopy groups\cdots \to \pi_(B) \to \pi_n(\text(f)) \to \pi_n(A) \to \pi_n(B) \to \cdotsMoreover, the homotopy fiber can be found in other contexts, such as homological algebra, where the distinguished triangleC(f)_\bullet 1\to A_\bullet \to B_\bullet \xrightarrowgives a long exact sequence analogous to the long exact sequence of homotopy groups. There is a dual construction called the homotopy cofiber. Construction The homotopy fiber has a simple description for a continuous map f:A \to B. If we replace f by a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics with the major subdisciplines of number theory, algebra, geometry, and analysis, respectively. There is no general consensus among mathematicians about a common definition for their academic discipline. Most mathematical activity involves the discovery of properties of abstract objects and the use of pure reason to prove them. These objects consist of either abstractions from nature orin modern mathematicsentities that are stipulated to have certain properties, called axioms. A ''proof'' consists of a succession of applications of deductive rules to already established results. These results include previously proved theorems, axioms, andin case of abstraction from naturesome basic properties that are considered true starting points of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homotopy Group
In mathematics, homotopy groups are used in algebraic topology to classify topological spaces. The first and simplest homotopy group is the fundamental group, denoted \pi_1(X), which records information about loops in a space. Intuitively, homotopy groups record information about the basic shape, or '' holes'', of a topological space. To define the ''n''-th homotopy group, the base-point-preserving maps from an ''n''-dimensional sphere (with base point) into a given space (with base point) are collected into equivalence classes, called homotopy classes. Two mappings are homotopic if one can be continuously deformed into the other. These homotopy classes form a group, called the ''n''-th homotopy group, \pi_n(X), of the given space ''X'' with base point. Topological spaces with differing homotopy groups are never equivalent (homeomorphic), but topological spaces that homeomorphic have the same homotopy groups. The notion of homotopy of paths was introduced by Camille Jordan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adams Resolution
In mathematics, specifically algebraic topology, there is a resolution analogous to free resolutions of spectra yielding a tool for constructing the Adams spectral sequence. Essentially, the idea is to take a connective spectrum of finite type X and iteratively resolve with other spectra that are in the homotopy kernel of a map resolving the cohomology classes in H^*(X;\mathbb/p) using Eilenberg–MacLane spectra. This construction can be generalized using a spectrum E, such as the Brown–Peterson spectrum BP, or the complex cobordism spectrum MU, and is used in the construction of the Adams–Novikov spectral sequencepg 49. Construction The mod p Adams resolution (X_s,g_s) for a spectrum X is a certain "chain-complex" of spectra induced from recursively looking at the fibers of maps into generalized Eilenberg–Maclane spectra giving generators for the cohomology of resolved spectrapg 43. By this, we start by considering the map\begin X \\ \downarrow \\ K \endwhere K is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quasi-fibration
In algebraic topology, a quasifibration is a generalisation of fibre bundles and fibrations introduced by Albrecht Dold and René Thom. Roughly speaking, it is a continuous map ''p'': ''E'' → ''B'' having the same behaviour as a fibration regarding the (relative) homotopy groups of ''E'', ''B'' and ''p''−1(''x''). Equivalently, one can define a quasifibration to be a continuous map such that the inclusion of each fibre into its homotopy fibre is a weak equivalence. One of the main applications of quasifibrations lies in proving the Dold-Thom theorem. Definition A continuous surjective map of topological spaces ''p'': ''E'' → ''B'' is called a quasifibration if it induces isomorphisms : p_*\colon \pi_i(E,p^(x),y) \to \pi_i(B,x) for all ''x'' ∈ ''B'', ''y'' ∈ ''p''−1(''x'') and ''i'' ≥ 0. For ''i'' = 0,1 one can only speak of bijections between the two sets. By definition, quasifibrations share a key property of fibrations, namely that a quasifibration ''p'': ''E ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homotopy Cofiber
In mathematics, especially homotopy theory, the mapping cone is a construction C_f of topology, analogous to a quotient space. It is also called the homotopy cofiber, and also notated Cf. Its dual, a fibration, is called the mapping fibre. The mapping cone can be understood to be a mapping cylinder Mf, with one end of the cylinder collapsed to a point. Thus, mapping cones are frequently applied in the homotopy theory of pointed spaces. Definition Given a map f\colon X \to Y, the mapping cone C_f is defined to be the quotient space of the mapping cylinder (X \times I) \sqcup_f Y with respect to the equivalence relation \forall x,x' \in X, (x, 0) \sim \left(x', 0\right)\,, (x, 1) \sim f(x). Here I denotes the unit interval , 1with its standard topology. Note that some authors (like J. Peter May) use the opposite convention, switching 0 and 1. Visually, one takes the cone on ''X'' (the cylinder X \times I with one end (the 0 end) identified to a point), and glues the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Whitehead Tower
In homotopy theory, a branch of algebraic topology, a Postnikov system (or Postnikov tower) is a way of decomposing a topological space's homotopy groups using an inverse system of topological spaces whose homotopy type at degree k agrees with the truncated homotopy type of the original space X. Postnikov systems were introduced by, and are named after, Mikhail Postnikov. Definition A Postnikov system of a path-connected space X is an inverse system of spaces :\cdots \to X_n \xrightarrow X_\xrightarrow \cdots \xrightarrow X_2 \xrightarrow X_1 \xrightarrow * with a sequence of maps \phi_n\colon X \to X_n compatible with the inverse system such that # The map \phi_n\colon X \to X_n induces an isomorphism \pi_i(X) \to \pi_i(X_n) for every i\leq n. # \pi_i(X_n) = 0 for i > n. # Each map p_n\colon X_n \to X_ is a fibration, and so the fiber F_n is an Eilenberg–MacLane space, K(\pi_n(X),n). The first two conditions imply that X_1 is also a K(\pi_1(X),1)-space. More generally, i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Postnikov Tower
In homotopy theory, a branch of algebraic topology, a Postnikov system (or Postnikov tower) is a way of decomposing a topological space's homotopy groups using an inverse system of topological spaces whose homotopy type at degree k agrees with the truncated homotopy type of the original space X. Postnikov systems were introduced by, and are named after, Mikhail Postnikov. Definition A Postnikov system of a path-connected space X is an inverse system of spaces :\cdots \to X_n \xrightarrow X_\xrightarrow \cdots \xrightarrow X_2 \xrightarrow X_1 \xrightarrow * with a sequence of maps \phi_n\colon X \to X_n compatible with the inverse system such that # The map \phi_n\colon X \to X_n induces an isomorphism \pi_i(X) \to \pi_i(X_n) for every i\leq n. # \pi_i(X_n) = 0 for i > n. # Each map p_n\colon X_n \to X_ is a fibration, and so the fiber F_n is an Eilenberg–MacLane space, K(\pi_n(X),n). The first two conditions imply that X_1 is also a K(\pi_1(X),1)-space. More generally, i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mapping Cylinder
In mathematics, specifically algebraic topology, the mapping cylinder of a continuous function f between topological spaces X and Y is the quotient :M_f = (( ,1times X) \amalg Y)\,/\,\sim where the \amalg denotes the disjoint union, and ∼ is the equivalence relation generated by :(0,x)\sim f(x)\quad\textx\in X. That is, the mapping cylinder M_f is obtained by gluing one end of X\times ,1/math> to Y via the map f. Notice that the "top" of the cylinder \\times X is homeomorphic to X, while the "bottom" is the space f(X)\subset Y. It is common to write Mf for M_f, and to use the notation \sqcup_f or \cup_f for the mapping cylinder construction. That is, one writes :Mf = ( ,1times X) \cup_f Y with the subscripted cup symbol denoting the equivalence. The mapping cylinder is commonly used to construct the mapping cone Cf, obtained by collapsing one end of the cylinder to a point. Mapping cylinders are central to the definition of cofibrations. Basic properties The bottom ''Y'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mapping Cone (topology)
In mathematics, especially homotopy theory, the mapping cone is a construction C_f of topology, analogous to a quotient space. It is also called the homotopy cofiber, and also notated Cf. Its dual, a fibration, is called the mapping fibre. The mapping cone can be understood to be a mapping cylinder Mf, with one end of the cylinder collapsed to a point. Thus, mapping cones are frequently applied in the homotopy theory of pointed spaces. Definition Given a map f\colon X \to Y, the mapping cone C_f is defined to be the quotient space of the mapping cylinder (X \times I) \sqcup_f Y with respect to the equivalence relation \forall x,x' \in X, (x, 0) \sim \left(x', 0\right)\,, (x, 1) \sim f(x). Here I denotes the unit interval , 1with its standard topology. Note that some authors (like J. Peter May) use the opposite convention, switching 0 and 1. Visually, one takes the cone on ''X'' (the cylinder X \times I with one end (the 0 end) identified to a point), and glues the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weak Equivalence (homotopy Theory)
In mathematics, a weak equivalence is a notion from homotopy theory that in some sense identifies objects that have the same "shape". This notion is formalized in the axiomatic definition of a model category. A model category is a category with classes of morphisms called weak equivalences, fibrations, and cofibrations, satisfying several axioms. The associated homotopy category of a model category has the same objects, but the morphisms are changed in order to make the weak equivalences into isomorphisms. It is a useful observation that the associated homotopy category depends only on the weak equivalences, not on the fibrations and cofibrations. Topological spaces Model categories were defined by Quillen as an axiomatization of homotopy theory that applies to topological spaces, but also to many other categories in algebra and geometry. The example that started the subject is the category of topological spaces with Serre fibrations as fibrations and weak homotopy equivalen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Puppe Sequence
In mathematics, the Puppe sequence is a construction of homotopy theory, so named after Dieter Puppe. It comes in two forms: a long exact sequence, built from the mapping fibre (a fibration), and a long coexact sequence, built from the mapping cone (which is a cofibration). Joseph J. Rotman, ''An Introduction to Algebraic Topology'' (1988) Springer-Verlag ''(See Chapter 11 for construction.)'' Intuitively, the Puppe sequence allows us to think of homology theory as a functor that takes spaces to long-exact sequences of groups. It is also useful as a tool to build long exact sequences of relative homotopy groups. Exact Puppe sequence Let f\colon (X,x_0)\to(Y,y_0) be a continuous map between pointed spaces and let Mf denote the mapping fibre (the fibration dual to the mapping cone). One then obtains an exact sequence: :Mf\to X \to Y where the mapping fibre is defined as: :Mf = \ Observe that the loop space \Omega Y injects into the mapping fibre: \Omega Y \to Mf, as i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Five Lemma
In mathematics, especially homological algebra and other applications of abelian category theory, the five lemma is an important and widely used lemma about commutative diagrams. The five lemma is not only valid for abelian categories but also works in the category of groups, for example. The five lemma can be thought of as a combination of two other theorems, the four lemmas, which are dual to each other. Statements Consider the following commutative diagram in any abelian category (such as the category of abelian groups or the category of vector spaces over a given field) or in the category of groups. : file:5 lemma.svg The five lemma states that, if the rows are exact, ''m'' and ''p'' are isomorphisms, ''l'' is an epimorphism, and ''q'' is a monomorphism, then ''n'' is also an isomorphism. The two four-lemmas state: Proof The method of proof we shall use is commonly referred to as diagram chasing. We shall prove the five lemma by individually proving each of the two fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
