added if case for 'x' in function for difference_of_simplified_exponential_functions

src/main/py/read_math_function.py

@@ -128,3 +128,6 @@ def difference_of_simplified_exponential_functions(type, function):
     minuend, subtrahend = function.split('-')
     new_minuend = simplify_exponential_function('e', minuend)
     new_subtrahend = simplify_exponential_function('e', subtrahend)
+    if new_minuend != "Der Ausdruck muss die Variable 'x' enthalten." and new_subtrahend != "Der Ausdruck muss die Variable 'x' enthalten.":
+        simplified = new_minuend - new_subtrahend
+        return simplified