Monoid
a category with single object
associative magma with identity
a1 = 1a = a & (ab)c = a(bc)
wikipedia https://en.wikipedia.org/wiki/Monoid
The term monoid in this sense is first used by Nicolas Bourbaki. ref: https://mathoverflow.net/questions/338281/who-invented-monoid
order 2
cyclic group
(1, a): aa = a
#Math