Update app.py

app.py

@@ -30,6 +30,8 @@ request_history = deque(maxlen=1000)
 SYMPY_GUIDELINES = """
 When writing SymPy code to verify solutions:
 
+NOTE: For eigenvalue problems, use 'lam = Symbol('lam')' instead of importing from sympy.abc
+
 1. Variable Declaration and Expressions:
    - ALWAYS create symbolic expressions instead of literal numbers when working with mathematical operations:
      ```python