Columbia subject headings:
Harvard subject headings:
Eckert, Georg, 1912---Congresses.
Education--Germany--History--Congresses.
Socialism--Germany--History--Congresses.
Socialists--Germany--Congresses.
Princeton subject headings:
Eckert, Georg, 1912---Congresses.
Education--Germany--History--Congresses.
Socialism--Germany--Congresses.
Socialists--Germany--Congresses.