Columbia subject headings:
Coal mines and mining--France--Nord-Pas-de-Calais--History--Congresses.
Nord-Pas-de-Calais (France)--Economic conditions--20th century--Congresses.
Nord-Pas-de-Calais (France)--Social conditions--20th century--Congresses.
Harvard subject headings:
Coal mines and mining--France--Nord-Pas-de-Calais--History--Congresses.
Nord-Pas-de-Calais (France)--Economic conditions--20th century--Congresses.
Nord-Pas-de-Calais (France)--Social conditions--20th century--Congresses.
Princeton subject headings:
Coal mines and mining--France--Nord-Pas-de-Calais--History--Congresses.
Nord-Pas-de-Calais (France)--Economic conditions--20th century--Congresses.
Nord-Pas-de-Calais (France)--Social conditions--20th century--Congresses.