Columbia subject headings:
Harvard subject headings:
Business enterprises--Spain--País Vasco--History.
ETA (Organization)--History.
Extortion--Spain--País Vasco--History.
Terrorism--Economic aspects--Spain--País Vasco.
Princeton subject headings:
ETA (Organization)--History.
Extortion--Spain--País Vasco--History.
Terrorism--Economic aspects--Spain--País Vasco--History.