@@ -186,6 +186,11 @@ Of the various types, there are three atomic types, ~<number>~, ~<variable>~ and
(defmethod atomicp ((expression <atomic>))
(declare (ignore expression))
t)
+
+ (defmethod subsitute-expression (expression with (in <atomic>))
+ (if (eqal expression in)
+ with
+ in))
#+END_SRC
*** DONE Numbers