added calculation using simplify_exponential_function for difference_of_simplified_exponential_functions

src/main/py/read_math_function.py

@@ -125,4 +125,6 @@ def sum_of_simplified_exponential_functions(type, function):
 def difference_of_simplified_exponential_functions(type, function):
     if type !="de":
         return False
-    minuend, subtrahend = function.split('-')
+    minuend, subtrahend = function.split('-')
+    new_minuend = simplify_exponential_function('e', minuend)
+    new_subtrahend = simplify_exponential_function('e', subtrahend)