+
+;; - and / work differently from the above macro.
+;; If only one arg is given, it negates it or takes its reciprocal.
+;; Otherwise all the other args are subtracted from or divided by it.
+;; TODO: Use MACROLET when it exists
+(defmacro define-sub-or-div (operator unary-form)
+ `(defun ,operator (x &rest args)
+ (cond
+ ((null args) ,unary-form)
+ (t (dolist (y args)
+ (setq x (,operator x y)))
+ x))))
+
+(define-sub-or-div - (- x))
+(define-sub-or-div / (/ 1 x))