added selector difference_of_simplified_exponential_functions

src/main/py/read_math_function.py

@@ -23,6 +23,8 @@ def read_math_function():
                 simplified = simplify_exponential_function(type, function)
             elif type == "se":
                 simplified = sum_of_simplified_exponential_functions(type, function)
+            elif type == "de":
+                simplified = difference_of_simplified_exponential_functions(type, function)
             if not simplified:
                 print(
                     "Die eingegebene Funktion war ungültig, entspricht nicht der vorgegebenen Syntax"