Columbia subject headings:
Harvard subject headings:
Espionage--Portugal--History--20th century.
Nigeria--History--Civil War, 1967-1970
Nigeria--Relations--Portugal.
Portugal--Relations--Nigeria.
Princeton subject headings:
Espionage--Portugal--History--20th century.
Nigeria--History--Civil War, 1967-1970.
Nigeria--Relations--Portugal.
Portugal--Relations--Nigeria.