Columbia subject headings:
Labriola, Antonio, 1843-1904.
Philosophers--Italy--Correspondence.
Harvard subject headings:
Labriola, Antonio, 1843-1904.
Labriola, Antonio, 1843-1904. Correspondence.
Philosophers--Italy--Correspondence
Princeton subject headings:
Labriola, Antonio, 1834-1904--Correspondence.
Philosophers--Italy--Correspondence.
Socialists--Italy--Correspondence.