Hs-semigroups

Anything that associates

In mathematics, a semigroup is an algebraic structure consisting of a set together with an associative binary operation. A semigroup generalizes a monoid in that there might not exist an identity element. It also originally generalized a group a monoid with all inverses to a type where every element did not have to have an inverse, thus the name semigroup.

WWW https//github.com/ekmett/semigroups