Columbia subject headings:
Duty-free importation--Law and legislation--Canada.
Duty-free importation--Law and legislation--United States.
Tariff--Law and legislation--Canada.
Tariff--Law and legislation--United States.
Harvard subject headings:
Duty-free importation--Law and legislation--Canada.
Duty-free importation--Law and legislation--United States.
Free trade--Canada
Free trade--United States
Tariff--Law and legislation--Canada.
Tariff--Law and legislation--United States.
Princeton subject headings: