olemus
ühe binaarse tehtega algebraline süsteem,
näiteks rühm

=
an algebraic structure consisting of a set with a single binary operation acting on it

ülevaateid
http://mathworld.wolfram.com/Groupoid.html

https://en.wikipedia.org/wiki/Groupoid

https://math.tecnico.ulisboa.pt/seminars/download.php?fid=92

http://im0.p.lodz.pl/~kubarski/BCP76/PRADINES.pdf