(note TQG3_SIGNUM_MINIMAL)
(category general)

(instance Number3-1 NonnegativeRealNumber)

(=>
  (instance ?X NonnegativeRealNumber)
  (or
    (equal (SignumFn ?X) 0)
    (equal (SignumFn ?X) 1)))

(=>
  (instance ?X NegativeRealNumber)
  (equal (SignumFn ?X) -1))

(not
  (equal -1 0))

(not
  (equal -1 1))

(query
  (not
    (instance Number3-1 NegativeRealNumber)))

(answer yes)