منابع مشابه
Cohomology and Obstructions: Commutative Algebras
Associated with each of the classical cohomology theories in algebra has been a theory relating H (H as classically numbered) to obstructions to non-singular extensions and H with coefficients in a “center” to the non-singular extension theory (see [Eilenberg & MacLane (1947), Hochschild (1947), Hochschild (1954), MacLane (1958), Shukla (1961), Harrison (1962)]). In this paper we carry out the ...
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Let D be a small category. We define a variety of cohomology objects. Each starts with a functor to a category of " coefficents, " and produces a different sort of object as output. The coefficient categories are: sets Set, groups Gp, abelian groups Ab, and " bands " HGp, that is, the category whose objects are groups and whose morphisms are conjugacy classes of homomorphisms. Let S : D → Set b...
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Suppose that K ⊆ G is a graph embedded in some surface and F is a face of K with singular branches e and f such that F ∪ ∂F is homeomorphic to the torus minus an open disk. An embedding extension of K to G is a simple embedding if each K-bridge embedded in F is attached to at most one appearance of e and at most one appearance of f on ∂F . Combinatorial structure of minimal obstructions for exi...
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ژورنال
عنوان ژورنال: Journal of Pure and Applied Algebra
سال: 2011
ISSN: 0022-4049
DOI: 10.1016/j.jpaa.2010.09.003