Columbia subject headings:
Composers--Austria--Correspondence.
Mahler, Gustav, 1860-1911--Correspondence.
Harvard subject headings:
Composers--Austria--Correspondence
Conductors (Music)--Netherlands--Correspondence.
Mahler, Gustav, 1860-1911--Correspondence.
Mengelberg, Willem, 1871-1951--Correspondence.
Princeton subject headings:
Composers--Austria--Correspondence.
Mahler, Gustav, 1860-1911--Performances--Netherlands.