Columbia subject headings:
Communism--Portugal--History--20th century--Congresses.
Communism--Spain--History--20th century--Congresses.
Democratization--Portugal--History--20th century--Congresses.
Democratization--Spain--History--20th century--Congresses.
Left-wing extremists--Portugal--History--20th century--Congresses.
Left-wing extremists--Spain--History--20th century--Congresses.
Portugal--Politics and government--20th century--Congresses.
Radicalism--Portugal--History--20th century--Congresses.
Radicalism--Spain--History--20th century--Congresses.
Spain--Politics and government--20th century--Congresses.
Harvard subject headings:
Communism--Portugal--History--20th century--Congresses.
Communism--Spain--History--20th century--Congresses.
Left-wing extremists--Portugal--History--20th century--Congresses.
Left-wing extremists--Spain--History--20th century--Congresses.
Portugal--Politics and government--20th century--Congresses.
Radicalism--Portugal--History--20th century--Congresses.
Radicalism--Spain--History--20th century--Congresses.
Spain--Politics and government--20th century--Congresses.
Princeton subject headings:
Communism--Portugal--History--20th century--Congresses.
Communism--Spain--History--20th century--Congresses.
Left-wing extremists--Portugal--History--20th century--Congresses.
Left-wing extremists--Spain--History--20th century--Congresses.
Portugal--Politics and government--20th century--Congresses.
Radicalism--Portugal--History--20th century--Congresses.
Radicalism--Spain--History--20th century--Congresses.
Spain--Politics and government--20th century--Congresses.