Update app.py

app.py

@@ -58,13 +58,19 @@ def solve_polynomial(image, llm_url):
         try:
             expr = parse_latex(cleaned_latex)
         
-            # Trigger fallback if not a polynomial (i.e., not a SymPy Equality with a polynomial lhs - rhs)
+            # Trigger fallback if not a polynomial
             if not isinstance(expr, sp.Equality):
                 raise ValueError("Expression is not an equation.")
         
             lhs_minus_rhs = expr.lhs - expr.rhs
             if not lhs_minus_rhs.is_polynomial():
                 raise ValueError("Expression is not a polynomial.")
+            
+            # 🔍 Fallback trigger if junk variables found
+            junk_symbols = {"pm", "cdot", "mathrm", "boldmath", "bar", "L"}
+            symbols = {str(s) for s in expr.free_symbols}
+            if symbols & junk_symbols:
+                raise ValueError("Expression contains junk symbols.")
         
         except Exception:
             # Fallback to LLM microservice
@@ -73,17 +79,20 @@ def solve_polynomial(image, llm_url):
             try:
                 expr = parse_latex(cleaned_latex)
         
-                # Try again: check if fallback result is polynomial
                 if not isinstance(expr, sp.Equality):
                     raise ValueError("Expression is not an equation.")
         
                 lhs_minus_rhs = expr.lhs - expr.rhs
                 if not lhs_minus_rhs.is_polynomial():
                     raise ValueError("Expression is not a polynomial.")
+                
+                # 🔁 Fallback again if junk remains
+                symbols = {str(s) for s in expr.free_symbols}
+                if symbols & junk_symbols:
+                    raise ValueError("Expression contains junk symbols.")
             except Exception:
                 expr = None
 
-
         if expr is None:
             return (
                 "❌ Could not parse expression even after fallback:\n\n"