(
  (GIVEN w x y z)
  
    (= x2 (sqr x))
    (= wz (* w z))
    (= f (- wz x2))            ; deg = 2
    
    ; Clipping planes:
    
    (= wt (+ w w))
    
    (= py (* (- y wt) (+ y wt))) ; deg = 2
    
    (= px (* (- x wt) (+ x wt))) ; deg = 2
    
  (RETURN (max (max px py) f))
)