(defun c:fplot (/ res start x step ce) 
  (setq res 150
        start -5.0
        x start 
        step (/ 10.0 (float res)) 
        i 0) 
  (setq ce (getvar "cmdecho")) 
  (setvar "cmdecho" 0) 
  (command "3Dmesh" res res) 
  (while (< i (1+ res)) 
    (setq j 0 
          y start) 
    (while (< j res) 
      (setq j (1+ j) 
            y (+ y step)) 
(setq a (- (- x (expt x 3.0)) (expt y 3.0)))
(setq b (exp (/ (+ (* x x) (* y y)) -8.0)))
(setq c (exp (- (* x (* -1.0 x)) (/ (* y y) 4))))
(setq z (- (+ (* (* 0.28 a) b) c) 0.1))
(if (< z 0) (setq z 0))
      (command (list x y z)) 
    ) 
    (setq i (1+ i) 
          x (+ x step)) 
  ) 
  (setvar "cmdecho" ce) 
)