18-04 Explicit machine computation and programs (not the theory of computation or programming)

18-06 Proceedings, conferences, collections, etc.

18Axx General theory of categories and functors

18A10 Graphs, diagram schemes, precategories [See especially <a href="#code:20L05">20L05</a>]

18A15 Foundations, relations to logic and deductive systems [See also <a href="#code:03-XX">03-XX</a>]

18A20 Epimorphisms, monomorphisms, special classes of morphisms, null morphisms

18A22 Special properties of functors (faithful, full, etc.)

18A23 Natural morphisms, dinatural morphisms

18A25 Functor categories, comma categories

18A30 Limits and colimits (products, sums, directed limits, pushouts, fiber products, equalizers, kernels, ends and coends, etc.)

18A32 Factorization of morphisms, substructures, quotient structures, congruences, amalgams

18A35 Categories admitting limits (complete categories), functors preserving limits, completions

18A40 Adjoint functors (universal constructions, reflective subcategories, Kan extensions, etc.)

18A99 None of the above, but in this section

18B05 Category of sets, characterizations [See also <a href="#code:03-XX">03-XX</a>]

18B10 Category of relations, additive relations

18B15 Embedding theorems, universal categories [See also <a href="#code:18E20">18E20</a>]

18B20 Categories of machines, automata, operative categories [See also <a href="#code:03D05">03D05</a>, <a href="#code:68Qxx">68Qxx</a>]

18B25 Topoi [See also <a href="#code:03G30">03G30</a>]

18B30 Categories of topological spaces and continuous mappings [See also <a href="#code:54-XX">54-XX</a>]

18B35 Preorders, orders and lattices (viewed as categories) [See also <a href="#code:06-XX">06-XX</a>]

18B40 Groupoids, semigroupoids, semigroups, groups (viewed as categories) [See also <a href="#code:20Axx">20Axx</a>, <a href="#code:20L05">20L05</a>, <a href="#code:20Mxx">20Mxx</a>]

18B99 None of the above, but in this section

18C05 Equational categories [See also <a href="#code:03C05">03C05</a>, <a href="#code:08C05">08C05</a>]