Columbia subject headings:
German literature--Germany--Ruhr (Region)--History and criticism.
Harvard subject headings:
German literature--19th century--Themes, motives--Congresses.
Industries in literature--Congresses.
Ruhr (Germany : Region)--In literature--Congresses.
Princeton subject headings:
German literature--19th century--History and criticism--Congresses.
German literature--20th century--History and criticism--Congresses.
Industries in literature--Congresses.
Ruhr (Germany : Region)--In literature--Congresses.