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} 


1800 
General reference works (handbooks, dictionaries, bibliographies, etc.) 


1801 
Instructional exposition (textbooks, tutorial papers, etc.) 


1802 
Research exposition (monographs, survey articles) 


1803 
Historical (must also be assigned at least one classification number from Section 01) 


1804 
Explicit machine computation and programs (not the theory of computation or programming) 


1806 
Proceedings, conferences, collections, etc. 

18Axx 

General theory of categories and functors 

18Bxx 

Special categories 

18Cxx 

Categories and theories 

18Dxx 

Categories with structure 

18Exx 

Abelian categories 

18Fxx 

Categories and geometry 

18Gxx 

Homological algebra [See also 13Dxx, 16Exx, 20Jxx, 55Nxx, 55Uxx, 57Txx] 