Columbia subject headings:
Harvard subject headings:
Constitutional history--Puerto Rico--Sources.
Puerto Rico--Foreign relations--United States--Sources.
Puerto Rico--Politics and government--1952---Sources.
Referendum--Puerto Rico.
United States--Foreign relations--Puerto Rico--Sources.
Princeton subject headings:
Puerto Rico--Politics and government--1952-1998.
Puerto Rico--Relations--United States.
United States--Relations--Puerto Rico.