20Lxx Groupoids (i.e. small categories in which all morphisms are isomorphisms), {For sets with a single binary operation, See 20N02; for topological groupoids, See 22A22, 58H05} ( 0 Dok. )

• 20L05 General theory ( 0 Dok. )
• 20L10 Connections with group theory ( 0 Dok. )
• 20L13 Mappings of groupoids ( 0 Dok. )
• 20L15 Connections with topology ( 0 Dok. )
• 20L17 Connections with category theory ( 0 Dok. )
• 20L99 None of the above but in this section ( 0 Dok. )