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Standard complex

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(Redirected from Bar construction)

In mathematics, the standard complex, also called standard resolution, bar resolution, bar complex, bar construction, is a way of constructing resolutions in homological algebra. It was first introduced for the special case of algebras over a commutative ring by Samuel Eilenberg and Saunders Mac Lane (1953) and Henri Cartan and Eilenberg (1956, IX.6) and has since been generalized in many ways.

The name "bar complex" comes from the fact that Eilenberg & Mac Lane (1953) used a vertical bar | as a shortened form of the tensor product in their notation for the complex.

Definition

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If A is an associative algebra over a field K, the standard complex is

with the differential given by

If A is a unital K-algebra, the standard complex is exact. Moreover, is a free A-bimodule resolution of the A-bimodule A.

Normalized standard complex

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The normalized (or reduced) standard complex replaces with .

Monads

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See also

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References

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  • Cartan, Henri; Eilenberg, Samuel (1956), Homological algebra, Princeton Mathematical Series, vol. 19, Princeton University Press, ISBN 978-0-691-04991-5, MR 0077480
  • Eilenberg, Samuel; Mac Lane, Saunders (1953), "On the groups of . I", Annals of Mathematics, Second Series, 58: 55–106, doi:10.2307/1969820, ISSN 0003-486X, JSTOR 1969820, MR 0056295
  • Ginzburg, Victor (2005). "Lectures on Noncommutative Geometry". arXiv:math.AG/0506603.