added if not check for simplify_product_function

src/main/py/read_math_function.py

@@ -100,3 +100,5 @@ def simplify_product_function(type, function):
     result_variables = ""
     for term in terms:
         simplified_term = simplify_easy_math_function("v", term.strip())
+        if not simplified_term or len(simplified_term) != 2:
+            return False