Columbia subject headings:
Admission of nonimmigrants--United States.
Customs administration--Law and legislation--United States.
Emigration and immigration law--United States.
Freedom of movement--United States.
Harvard subject headings:
Admission of nonimmigrants--United States.
Customs administration--Law and legislation--United States.
Emigration and immigration law--United States.
Freedom of movement--United States.
Princeton subject headings:
Admission of nonimmigrants--United States.
Customs administration--Law and legislation--United States.
Emigration and immigration law--United States.
Freedom of movement--United States.