20XX 


Group theory and generalizations 

20Kxx 

Abelian groups 


20K01 
Finite abelian groups 


20K10 
Torsion groups, primary groups and generalized primary groups 


20K15 
Torsionfree groups, finite rank 


20K20 
Torsionfree groups, infinite rank 


20K21 
Mixed groups 


20K25 
Direct sums, direct products, etc. 


20K27 
Subgroups 


20K30 
Automorphisms, homomorphisms, endomorphisms, etc. 


20K35 
Extensions 


20K40 
Homological and categorical methods 


20K45 
Topological methods [See also 22A05, 22B05] 


20K99 
None of the above, but in this section 