Update app.py

app.py

@@ -93,9 +93,9 @@ async def init():
 
 @cl.on_message
 async def main(message):
-    global last_response
-
+   
     chain = cl.user_session.get("chain")
+    
     cb = cl.AsyncLangchainCallbackHandler(
         stream_final_answer=True, 
         answer_prefix_tokens=["FINAL", "ANSWER"]
@@ -106,7 +106,7 @@ async def main(message):
     
     answer = res["result"]
     source_elements = []
-    visited_sources = set()
+    visited_sources = set(0)
 
     docs = res.get("source_documents", [])
     metadatas = [doc.metadata for doc in docs]