20XX 


Group theory and generalizations 

20Mxx 

Semigroups 


20M05 
Free semigroups, generators and relations, word problems [See also 03D40, 08A50, 20F10] 


20M07 
Varieties and pseudovarieties of semigroups 


20M10 
General structure theory 


20M11 
Radical theory 


20M12 
Ideal theory 


20M13 
Arithmetic theory of monoids 


20M14 
Commutative semigroups 


20M15 
Mappings of semigroups 


20M17 
Regular semigroups 


20M18 
Inverse semigroups 


20M19 
Orthodox semigroups 


20M20 
Semigroups of transformations, etc. [See also 47D03, 47H20, 54H15] 


20M25 
Semigroup rings, multiplicative semigroups of rings [See also 16S36, 16Y60] 


20M30 
Representation of semigroups; actions of semigroups on sets 


20M32 
Algebraic monoids 


20M35 
Semigroups in automata theory, linguistics, etc. [See also 03D05, 68Q70, 68T50] 


20M50 
Connections of semigroups with homological algebra and category theory 


20M99 
None of the above, but in this section 