olemus
rühmoid, mille binaartehe on assotsiatiivne

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

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

http://planetmath.org/examplesofsemigroups

https://www-users.york.ac.uk/~varg1/SemigroupTheory.pdf

https://www.math.unl.edu/~jmeakin2/groups%20and%20semigroups.pdf

https://www.goodreads.com/shelf/show/semigroups

rakendusi
https://globaljournals.org/GJSFR_Volume15/3-Applications-of-Semigroups.pdf

https://shannoninstitute.ucd.ie/~semiring/diss_oliver.pdf