https://hp-agda-unimath-vojtechstep.netlify.app/archive/hp-agda-unimath/group-theory.submonoids.html
Submonoids - agda-unimath
agda
https://hp-agda-unimath-vojtechstep.netlify.app/archive/hp-agda-unimath/group-theory.normal-submonoids-commutative-monoids.html
Normal submonoids of commutative monoids - agda-unimath
normalcommutativeagda