Columbia subject headings:
Communists--Italy--Congresses.
Labor leaders--Italy--Congresses.
Trentin, Bruno--Congresses.
Harvard subject headings:
Communists--Italy--Congresses.
Labor leaders--Italy--Congresses.
Trentin, Bruno--Congresses.
Princeton subject headings:
Labor leaders--Italy--Biography--Congresses.
Right and left (Political science)--France--History--20th century--Congresses.
Right and left (Political science)--Italy--History--20th century--Congresses.
Syndicalism--Italy--History--20th century--Congresses.
Trentin, Bruno--Congresses.