Columbia subject headings:
Duty-free importation--Gabon.
Duty-free importation--Mongolia.
Tariff preferences--Law and legislation--United States.
United States--Commercial policy.
Harvard subject headings:
Duty-free importation--Gabon.
Duty-free importation--Mongolia.
Tariff preferences--Law and legislation--United States.
United States--Commercial policy.
Princeton subject headings: