18XX 


Category theory; homological algebra {For commutative rings see 13Dxx, for associative rings 16Exx, for groups 20Jxx, for topological groups and related structures 57Txx; see also 55Nxx and 55Uxx for algebraic topology} 

18Bxx 

Special categories 


18B05 
Category of sets, characterizations [See also 03XX] 


18B10 
Category of relations, additive relations 


18B15 
Embedding theorems, universal categories [See also 18E20] 


18B20 
Categories of machines, automata, operative categories [See also 03D05, 68Qxx] 


18B25 
Topoi [See also 03G30] 


18B30 
Categories of topological spaces and continuous mappings [See also 54XX] 


18B35 
Preorders, orders and lattices (viewed as categories) [See also 06XX] 


18B40 
Groupoids, semigroupoids, semigroups, groups (viewed as categories) [See also 20Axx, 20L05, 20Mxx] 


18B99 
None of the above, but in this section 