Columbia subject headings:
Licenses--United States.
Occupations--United States.
Professions--United States.
Harvard subject headings:
Licenses--United States.
Occupations--Licenses--United States.
Occupations--United States
Professions--Licenses--United States.
Professions--United States.
Princeton subject headings:
Licenses--United States.
Occupations--United States.
Professions--United States.