Columbia subject headings:
Canada--Commerce--United States.
Free trade--Canada.
Free trade--Mexico.
Free trade--United States.
Mexico--Commerce--United States.
United States--Commerce--Canada.
United States--Commerce--Mexico.
Harvard subject headings:
Canada--Commerce--United States.
Free trade--Canada
Free trade--Mexico
Free trade--United States
Mexico--Commerce--United States.
United States--Commerce--Canada.
United States--Commerce--Mexico.
Princeton subject headings:
Canada--Commerce--United States.
Free trade--Canada.
Free trade--Mexico.
Free trade--United States.
Mexico--Commerce--United States.
United States--Commerce--Canada.
United States--Commerce--Mexico.