(.module:
  [library
   [lux (#- and)]])

(interface: .public (Monoid a)
  (: a
     identity)
  (: (-> a a a)
     composite))

(def: .public (and left right)
  (All [l r] (-> (Monoid l) (Monoid r) (Monoid [l r])))
  (implementation
   (def: identity
     [(\ left identity) (\ right identity)])
   
   (def: (composite [lL rL] [lR rR])
     [(\ left composite lL lR)
      (\ right composite rL rR)])))