typeclass Copy =
  & copy : Copy -> Copy

typeclass (Ord : #Eq) =
  & ( < ) : Ord -> Ord -> Bool
  & ( > ) : Ord -> Ord -> Bool
  & ( <= ) : Ord -> Ord -> Bool
  & ( >= ) : Ord -> Ord -> Bool

typeclass (D : #A #B #C) 'A 'B =
  & do_something : Unit -> (& 'A & 'B)

typeclass E 'A =
  & do_something : Unit -> 'A

namespace const ord : Ord {
  def ( <= ) : a b = (a < b) || (a == b)
  def ( > ) : a b = !(a <= b)
  def ( >= ) : a b = !(a < b)
}