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KERNELS OF MORPHISMS BETWEEN INDECOMPOSABLE INJECTIVE MODULES

Published online by Cambridge University Press:  24 June 2010

ALBERTO FACCHINI
Affiliation:
Dipartimento di Matematica Pura e Applicata, Università di Padova, 35131 Padova, Italy e-mail: facchini@math.unipd.it
ŞULE ECEVIT
Affiliation:
Department of Mathematics, Gebze Institute of Technology, Çayirova Campus, 41400 Gebze-Kocaeli, Turkey e-mail: secevit@gyte.edu.tr, mtkosan@gyte.edu.tr
M. TAMER KOŞAN
Affiliation:
Department of Mathematics, Gebze Institute of Technology, Çayirova Campus, 41400 Gebze-Kocaeli, Turkey e-mail: secevit@gyte.edu.tr, mtkosan@gyte.edu.tr
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Abstract

We show that the endomorphism rings of kernels ker ϕ of non-injective morphisms ϕ between indecomposable injective modules are either local or have two maximal ideals, the module ker ϕ is determined up to isomorphism by two invariants called monogeny class and upper part, and a weak form of the Krull–Schmidt theorem holds for direct sums of these kernels. We prove with an example that our pathological decompositions actually take place. We show that a direct sum of n kernels of morphisms between injective indecomposable modules can have exactly n! pairwise non-isomorphic direct-sum decompositions into kernels of morphisms of the same type. If ER is an injective indecomposable module and S is its endomorphism ring, the duality Hom(−, ER) transforms kernels of morphisms ERER into cyclically presented left modules over the local ring S, sending the monogeny class into the epigeny class and the upper part into the lower part.

Keywords

Type
Research Article
Copyright
Copyright © Glasgow Mathematical Journal Trust 2010

References

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