Columbia subject headings:
Free trade--Canada.
Free trade--Mexico.
Free trade--United States.
Harvard subject headings:
Canada--Foreign economic relations--Mexico.
Free ports and zones--North America.
Free trade--Mexico
Free trade--North America
Mexico--Commercial policy.
Mexico--Foreign economic relations--Canada.
Mexico--Foreign economic relations--United States.
United States--Foreign economic relations--Mexico.
Princeton subject headings:
Foreign trade regulation--Mexico.
Foreign trade regulation--United States.
Mexico--Economic conditions.
Mexico--Foreign economic relations--United States.
United States--Foreign economic relations--Mexico.