(defun proced-< (num1 num2)
"Return t if NUM1 less than NUM2.
-Return `equal' if NUM1 equals NUM2. Return nil if NUM1 greater than NUM2."
- (if (= num1 num2)
- 'equal
- (< num1 num2)))
+Return `equal' if NUM1 equals NUM2. Return nil if NUM1 greater than NUM2.
+If either NUM1 or NUM2 is not a number, return nil."
+ (when (and (numberp num1) (numberp num2))
+ (if (= num1 num2)
+ 'equal
+ (< num1 num2))))
(defun proced-string-lessp (s1 s2)
"Return t if string S1 is less than S2 in lexicographic order.