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Lecture# Cohomology Groups: Hopf Formula

Description

This lecture covers the Hopf formula in cohomology groups, focusing on the 4-term exact sequence and the Hopf formula theorem. It explains the concepts of kernel, subgroup, and conjugation, leading to the identification of the cohomology groups. The lecture delves into the Hopf formula's implications and applications, illustrating the isomorphism between different groups and the significance of exact sequences in cohomology. It concludes with a discussion on homology with arbitrary coefficients and the relationship between group actions and cohomology.

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In course

Instructor

MATH-506: Topology IV.b - cohomology rings

Singular cohomology is defined by dualizing the singular chain complex for spaces. We will study its basic properties, see how it acquires a multiplicative structure and becomes a graded commutative a

Related concepts (319)

Sheaf (mathematics)

In mathematics, a sheaf (: sheaves) is a tool for systematically tracking data (such as sets, abelian groups, rings) attached to the open sets of a topological space and defined locally with regard to them. For example, for each open set, the data could be the ring of continuous functions defined on that open set. Such data is well behaved in that it can be restricted to smaller open sets, and also the data assigned to an open set is equivalent to all collections of compatible data assigned to collections of smaller open sets covering the original open set (intuitively, every piece of data is the sum of its parts).

Motivic cohomology

Motivic cohomology is an invariant of algebraic varieties and of more general schemes. It is a type of cohomology related to motives and includes the Chow ring of algebraic cycles as a special case. Some of the deepest problems in algebraic geometry and number theory are attempts to understand motivic cohomology. Let X be a scheme of finite type over a field k. A key goal of algebraic geometry is to compute the Chow groups of X, because they give strong information about all subvarieties of X.

Topology

In mathematics, topology (from the Greek words τόπος, and λόγος) is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing holes, opening holes, tearing, gluing, or passing through itself. A topological space is a set endowed with a structure, called a topology, which allows defining continuous deformation of subspaces, and, more generally, all kinds of continuity.

H

H, or h, is the eighth letter in the Latin alphabet, used in the modern English alphabet, including the alphabets of other western European languages and others worldwide. Its name in English is aitch (pronounced eɪtʃ, plural aitches), or regionally haitch heɪtʃ. The original Semitic letter Heth most likely represented the voiceless pharyngeal fricative (ħ). The form of the letter probably stood for a fence or posts. The Greek Eta 'Η' in archaic Greek alphabets, before coming to represent a long vowel, /ɛː/, still represented a similar sound, the voiceless glottal fricative /h/.

H-dropping

H-dropping or aitch-dropping is the deletion of the voiceless glottal fricative or "H-sound", [h]. The phenomenon is common in many dialects of English, and is also found in certain other languages, either as a purely historical development or as a contemporary difference between dialects. Although common in most regions of England and in some other English-speaking countries, and linguistically speaking a neutral evolution in languages, H-dropping is often stigmatized as a sign of careless or uneducated speech.

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