(in-package :maxima)

(defun pdiff-get-number-args (f)
  (let ((z (cdar (member f (cdr $functions) :key #'caar))))
    (cond ((and z (every #'symbolp z)) (length z))
	  ((and (atom f) (or (trigp f) (arcp f) (memq f '(%log %gamma %erf %sqrt mabs)))) 1)
	  ((memq f '($bessel_i $bessel_j $bessel_k $bessel_y)) 2)
	  ((or (equal f "^") (equal f ".") (equal f "^^")) 2)
	  ((and (op-equalp f 'lambda) (every #'symbolp (margs (second f))))
	   ($length (second f)))
	  ((and (symbolp f) (get f 'grad)) (length (first (get f 'grad))))
	  ((eq t ($constantp f)) 'constant-function)
	  (t nil))))