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} 

18Fxx 

Categories and geometry 


18F05 
Local categories and functors 


18F10 
Grothendieck topologies [See also 14F20] 


18F15 
Abstract manifolds and fiber bundles [See also 55Rxx, 57Pxx] 


18F20 
Presheaves and sheaves [See also 14F05, 32C35, 32L10, 54B40, 55N30] 


18F25 
Algebraic $K$theory and $L$theory [See also 11Exx, 11R70, 11S70, 12XX, 13D15, 14Cxx, 16E20, 19XX, 46L80, 57R65, 57R67] 


18F30 
Grothendieck groups [See also 13D15, 16E20, 19Axx] 


18F99 
None of the above, but in this section 