%-

; Klein 4-group
tydecl element = E | A | B | C

(:def mult
  (:lambda x element
    (:lambda y element
      (:match (x, y)
        [(E, x) x]
        [(x, E) x]
        [(A, A) E]
        [(A, B) C]
        [(A, C) B]
        [(B, A) C]
        [(B, B) E]
        [(B, C) A]
        [(C, A) B]
        [(C, B) A]
        [(C, C) E]
        ))))