Columbia subject headings:
Abel, Carl Andreas, 1907-1994--Exhibitions.
Photography, Artistic--Exhibitions.
Working class--Germany--Rhein-Main Region--Pictorial works--Exhibitions.
Working class--Germany--Ruhr (Region)--Pictorial works--Exhibitions.
Harvard subject headings:
Abel, Carl Andreas, 1907-1994--Exhibitions.
Industries--Pictorial works--Exhibitions.
Photography, Artistic--Exhibitions
Working class--Germany--Rhein-Main Region--Pictorial works--Exhibitions.
Working class--Germany--Ruhr (Region)--Pictorial works--Exhibitions.
Princeton subject headings:
Abel, Carl Andreas, 1907-1994--Exhibitions.
Industries--Pictorial works--Exhibitions.
Working class--Germany--Rhein-Main Region--Pictorial works--Exhibitions.
Working class--Germany--Ruhr Region--Pictorial works--Exhibitions.