Columbia subject headings:
Beckerath, Willy von--Correspondence.
Ophüls, G. (Gustav)--Correspondence.
Harvard subject headings:
Beckerath, Willy von--Correspondence.
Ophüls, G. (Gustav)--Correspondence.
Princeton subject headings:
Beckerath, Willy von--Correspondence.
Choral conductors--Germany--Correspondence.
Ophüls, G. (Gustav)--Correspondence.
Painters--Germany--Correspondence.