Columbia subject headings:
Harvard subject headings:
Cologne (Germany)--Church history--Congresses.
Cologne (Germany)--History--Congresses.
Cologne (Germany)--Relations--Germany--Prussia--Congresses.
Prussia (Germany)--History--Congresses.
Prussia (Germany)--Relations--Germany--Cologne--Congresses.
Rhineland (Germany)--History--Congresses.
Princeton subject headings:
Cologne (Germany)--History.
Cologne (Germany)--Relations--Germany--Prussia.
Cologne (Germany)--Social life and customs.
Prussia (Germany)--History--1815-1870.
Prussia (Germany)--History--1870-
Prussia (Germany)--Relations--Germany--Cologne.