Perhaps you should try some spelling variations:
international congresses » international congress, internationalen kongresses, international conferences
mathematicians hungary » mathematician lunar, mathematicians germany, mathematicians have
invited speakers » invited papers

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: list of international congresses of mathematicians hungary AND invited speakers.
• Adding a wildcard symbol may retrieve word variants: list of international congresses of mathematicians hungary and invited speakers*.