20Nxx Other generalizations of groups
- 20N02 Sets with a single binary operation (groupoids)
- 20N05 Loops, quasigroups, See also {05Bxx}
- 20N07 Mappings of loops
- 20N10 Ternary systems (heaps, semiheaps, heapoids, etc.)
- 20N15 $n$-ary systems
- 20N20 Hypergroups
- 20N25 Fuzzy groups, See also {04A72}
- 20N99 None of the above but in this section
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