Update tool.py

tool.py

@@ -4,6 +4,7 @@ from langchain_community.tools.tavily_search import TavilySearchResults
 from langchain_community.document_loaders.wikipedia import WikipediaLoader
 from langchain_community.document_loaders.arxiv import ArxivLoader
 from langchain_community.document_loaders.pubmed import PubMedLoader
+from typing import Optional
 
 ## Simple algebra tools
 @tool