(defun refinable(f)
  "
;; Examples:
 (refinable (lambda(x) (sin (/ x 2pi))))
 (xgobips_simple \"p1.ps\"  (rseq -3 3 1000) (refinable (lambda(x) (if (> x .25) 1 0))))
 (xgobips_simple \"p2.ps\"  (rseq -3 3 1000) (refinable (lambda(x) (if (> x .5) 1 0))))
 (xgobips_simple \"p3.ps\"  (rseq -3 3 1000) (refinable (lambda(x) (if (> x .75) 1 0))))
 (xgobips_simple \"p4.ps\"  (rseq -pi pi 1000) (refinable (lambda(x) (sin (* x 2pi)))))
 (xgobips_simple \"p5.ps\"  (rseq -pi pi 1000) (refinable (lambda(x) (sin (* x 4pi)))))
 (xgobips_simple \"p6.ps\"  (rseq -pi pi 1000) (refinable (lambda(x) (- 1 (cos (* x 4pi))))))

 (xgobips_simple \"p7.ps\"  (rseq  -3 4 1000) (refinable (lambda(x) (+ 1 (* 4 (- 1 x) x)))))
"
  (let* (
	  )
    (lambda(x)
      (cond
       ((and (>= x 0) (< x 1))
	(funcall f x)
	)
       ((>= x 1) 
	(- (funcall f (/ x 2)) (funcall f (- x 1)))
	)
       ((< x 0) 
	(- (funcall f (/ (+ x 1) 2)) (funcall f (+ x 1)))
	)
       (t (error "You should not see this: refinable.lsp"))
       )
      )
    )
  )
(try-out refinable)