Columbia subject headings:
Arnould, Maurice-A. (Maurice-Aurélien), 1914-
Ruelle, Pierre, 1911-1993.
Wallonia (Belgium)--Civilization.
Harvard subject headings:
Arnould, Maurice-A. (Maurice-Aurélien), 1914-
Ruelle, Pierre, 1911-
Wallonia (Belgium)--Civilization.
Princeton subject headings: