Columbia subject headings:
Portugal--Foreign relations--Spain--Congresses.
Spain--Foreign economic relations--Portugal--Congresses.
Spain--Foreign relations--Portugal--Congresses.
Harvard subject headings:
Portugal--Foreign economic relations--Spain--Congresses.
Portugal--Foreign relations--Spain--Congresses.
Spain--Foreign economic relations--Portugal--Congresses.
Spain--Foreign relations--Portugal--Congresses.
Princeton subject headings: