Fix app.py

app.py

@@ -48,7 +48,7 @@ st.markdown("This app uses [BM25](https://en.wikipedia.org/wiki/Okapi_BM25), all
 prompt = st.chat_input("Search anything...")
 
 if prompt:
-    results = retriever.invoke(user_query)
+    results = retriever.invoke(prompt)
     st.text(f"Top n {len(results)} related papers")
 
     for result in results: