A simple characterization of theories of varieties

[摘要] We answer the question of which theories in the sense of Gabriel and Ulmer give rise to (finitary, multi-sorted) varieties and exhibit the 2-category of varieties as a (non-full) bireflective sub-2-category of the 2-category of locally finitely presentable categories. A central role is played by those objects, which we call effective projectives, whose hom functors preserve coequalizers of reflexive graphs, (C) 2000 Academic Press.

[发布日期] 2000-11-15

[关键词] variety;locally finitely presentable;coequalizer completion;finitely cocomplete