Columbia subject headings:
Harvard subject headings:
Africa, West--History--Congresses.
Chad Basin--Antiquities--Congresses.
Chad Basin--Climate--Congresses.
Savannas--Africa, West--Congresses.
Princeton subject headings:
Africa, West--History--Congresses.
Chad Basin--Antiquities--Congresses.
Chad Basin--Climate--Congresses.
Savannas--Africa, West--Congresses.
Savannas--Environmental aspects--Africa, West--Congresses.