Columbia subject headings:
Hours of labor--Germany--History--19th century--Sources.
Hours of labor--Germany--History--20th century--Sources.
Harvard subject headings:
Hours of labor--Germany--History--19th century--Sources.
Hours of labor--Germany--History--20th century--Sources.
Princeton subject headings:
Hours of labor--Germany--History--19th century--Sources.
Hours of labor--Germany--History--20th century--Sources.