Columbia subject headings:
Harvard subject headings:
Breitkopf & Härtel--Records and correspondence.
Busoni, Ferruccio, 1866-1924--Correspondence.
Princeton subject headings:
Breitkopf & Härtel--Correspondence.
Busoni, Ferruccio, 1866-1924--Correspondence.
Composers--Italy--Correspondence.
Music publishers--Germany--Correspondence.
Personal correspondence.