Columbia subject headings:
Foreign workers--Puerto Rico--History.
Puerto Rico--Emigration and immigration--History.
Social classes--Puerto Rico--History.
Harvard subject headings:
Foreign workers--Puerto Rico--History.
Puerto Rico--Emigration and immigration--History.
Social classes--Puerto Rico--History.
Princeton subject headings:
Foreign workers--Puerto Rico--History.
Puerto Rico--Emigration and immigration--History.
Social classes--Puerto Rico--History.