Columbia subject headings:
Composers--Austria--Correspondence.
Mahler family--Correspondence.
Mahler, Gustav, 1860-1911--Correspondence.
Harvard subject headings:
Composers--Austria--Correspondence
Mahler family--Correspondence.
Mahler, Gustav, 1860-1911--Correspondence.
Princeton subject headings:
Mahler family--Correspondence.
Mahler, Gustav, 1860-1911--Correspondence.