EXACT SUBCATEGORIES, SUBFUNCTORS OF EXT, AND SOME APPLICATIONS

Abstrakt

Let (A,E) be an exact category. We establish basic results that allow one to identify sub(bi)functors of Ext(epsilon)(-,-) using additivity of numericalfunctions and restriction to subcategories.

We also study a small number ofthese new functors over commutative local rings in detail and find a range ofapplications from detecting regularity to understanding Ulrich modules.

Klíčová slova

• GROTHENDIECK GROUPS
• EXACT CATEGORIES
• EXTENSIONS
• COMPLEXES
• MODULES