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Modules, comodules and cotensor products over Frobenius algebras
Rings and Algebras · Submitted 8 Jun 1998
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We prove that the cotensor product M \Box N of a right A-module M and a left A-module N is isomorphic to the vector space of homomorphisms from a particular left A^e-module D to N \otimes M, viewed as a left A^e-module.
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The abstract, sentence by sentence
We characterize noncommutative Frobenius algebras A in terms of the existence of a coproduct which is a map of left A^e-modules. We show that the category of right (left) comodules over A, relative to this coproduct, is isomorphic to the category of right (left) modules. This isomorphism enables a reformulation of the cotensor product of Eilenberg and Moore as a functor of modules rather than comodules. We prove that the cotensor product M \Box N of a right A-module M and a left A-module N is isomorphic to the vector space of homomorphisms from a particular left A^e-module D to N \otimes M, viewed as a left A^e-module. Some properties of D are described. Finally, we show that when A is a symmetric algebra, the cotensor product M \Box N and its derived functors are given by the Hochschild cohomology over A of N \otimes M.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We characterize noncommutative Frobenius algebras A in terms of the existence of a coproduct which is a map of left A^e-modules. | result 0.52 | 0.92 | 0.24 | asserted 1.00 |
| s1 | We show that the category of right (left) comodules over A, relative to this coproduct, is isomorphic to the category of right (left) modules. | result 0.97 | 0.95 | 0.18 | asserted 1.00 |
| s2 | This isomorphism enables a reformulation of the cotensor product of Eilenberg and Moore as a functor of modules rather than comodules. | contribution 0.34 | 0.82 | 0.16 | asserted 1.00 |
| s3 | We prove that the cotensor product M \Box N of a right A-module M and a left A-module N is isomorphic to the vector space of homomorphisms from a particular left A^e-module D to N \otimes M, viewed as a left A^e-module. | result 0.97 | 0.93 | 0.39 | asserted 1.00 |
| s4 | Some properties of D are described. | contribution 0.66 | 0.84 | 0.03 | asserted 0.63 |
| s5 | Finally, we show that when A is a symmetric algebra, the cotensor product M \Box N and its derived functors are given by the Hochschild cohomology over A of N \otimes M. | result 0.99 | 0.93 | 0.25 | asserted 1.00 |
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Original abstract
We characterize noncommutative Frobenius algebras A in terms of the existence of a coproduct which is a map of left A^e-modules. We show that the category of right (left) comodules over A, relative to this coproduct, is isomorphic to the category of right (left) modules. This isomorphism enables a reformulation of the cotensor product of Eilenberg and Moore as a functor of modules rather than comodules. We prove that the cotensor product M \Box N of a right A-module M and a left A-module N is isomorphic to the vector space of homomorphisms from a particular left A^e-module D to N \otimes M, viewed as a left A^e-module. Some properties of D are described. Finally, we show that when A is a symmetric algebra, the cotensor product M \Box N and its derived functors are given by the Hochschild cohomology over A of N \otimes M.
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