Abstract
This chapter presents an excursion in abstract algebra. It begins with the notions of group, subgroup, direct sum, homomorphism, isomorphism, etc., their basic properties, and numerous examples. This is justified by the main aim of the chapter: to establish the decomposition of a finite abelian group as a direct sum of cyclic subgroups, which is very similar to the decomposition of a vector space as a direct sum of cyclic subspaces (the Jordan normal form of a linear transformation). Moreover, the final part of the chapter presents a more general fact—the decomposition of a finitely generated torsion module over a Euclidean ring as a direct sum of cyclic submodules, which contains the decomposition of a vector space and the decomposition of a finite abelian group as partial cases.
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Notes
- 1.
The identity element of a group is unique. Indeed, if there existed another identity element e′∈G, then by definition, we would have the equalities ee′=e′ and ee′=e, from which it follows that e=e′.
- 2.
Unfortunately, there is a certain amount of disagreement over terminology, of which the reader should be aware: above, we defined a transformation of a set as a bijective mapping into itself, while at the same time, a linear (or affine) transformation of a vector (or affine) space is not by definition necessarily bijective, and to have bijectivity here, it is necessary to specify that the transformations be nonsingular.
- 3.
Named in honor of the Norwegian mathematician Niels Henrik Abel (1802–1829).
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© 2012 Springer-Verlag Berlin Heidelberg
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Shafarevich, I.R., Remizov, A.O. (2012). Groups, Rings, and Modules. In: Linear Algebra and Geometry. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-30994-6_13
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DOI: https://doi.org/10.1007/978-3-642-30994-6_13
Publisher Name: Springer, Berlin, Heidelberg
Print ISBN: 978-3-642-30993-9
Online ISBN: 978-3-642-30994-6
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