Columbia subject headings:
Harvard subject headings:
Environmental protection--France--Lorraine--Congresses.
Environmental protection--Germany--Saarland--Congresses.
Environmental protection--Luxembourg--Congresses.
Lorraine (France)--Environmental conditions--Congresses.
Luxembourg--Environmental conditions--Congresses.
Saarland (Germany)--Environmental conditions--Congresses.
Princeton subject headings:
Environmental protection--France--Lorraine--Congresses.
Environmental protection--Germany--Saarland--Congresses.
Environmental protection--Luxembourg--Congresses.
Lorraine (France)--Environmental conditions--Congresses.
Luxembourg--Environmental conditions--Congresses.
Saarland (Germany)--Environmental conditions--Congresses.