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}
- 20L05 General theory
- 20L10 Connections with group theory
- 20L13 Mappings of groupoids
- 20L15 Connections with topology
- 20L17 Connections with category theory
- 20L99 None of the above but in this section
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