Page 11 - Textos de Matemática Vol. 45

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the abelian group structure which is given to some specific class of extensions (called special Schreier extensions) with abelian kernel in Mon and to the par- allel specific class in SRng. Chapter 8 gives a synthetic structural presentation of what is involved under the Schreier split epimorphic process. There is an Appendix which collects some basic categorical notations and facts.
The authors are grateful to Alfredo Costa for the careful reading of the preliminary version of this book.