AC, the axiom of choice, because of its non-constructive character, is the most controversial mathematical axiom, shunned by some, used indiscriminately by others.

A modern introduction to the theory of structures via the language of category theory. Unique to this book is the emphasis on concrete categories.

The book collects original research papers on applied categorical structures, most of which have been presented at the North-West European Category Seminar 2003 in Berlin.

Jahrhundert einen bedeutenden Einfluß ausgeübt. Daher erschien es geboten, ausführliche Kommentare beizufügen.

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