diff --git a/src/main/py/read_math_function.py b/src/main/py/read_math_function.py
index 18dce88..f0bf97f 100644
--- a/src/main/py/read_math_function.py
+++ b/src/main/py/read_math_function.py
@@ -124,4 +124,5 @@ def sum_of_simplified_exponential_functions(type, function):
 
 def difference_of_simplified_exponential_functions(type, function):
     if type !="de":
-        return False
\ No newline at end of file
+        return False
+    minuend, subtrahend = function.split('-')
\ No newline at end of file