Columbia subject headings:
Environmental law--Mexico.
Environmental law--United States.
Mexico--Foreign relations--United States.
United States--Foreign relations--Mexico.
Harvard subject headings:
Environmental law--Mexico
Environmental law--United States
Mexico--Foreign relations--United States.
United States--Foreign relations--Mexico.
Princeton subject headings:
Environmental law--Mexico.
Environmental law--United States.
Mexico--Foreign relations--United States.
United States--Foreign relations--Mexico.