Columbia subject headings:
Iselin, Isaak, 1728-1782--Correspondence.
Nicolai, Friedrich, 1733-1811--Correspondence.
Harvard subject headings:
Iselin, Isaak, 1728-1782--Correspondence.
Nicolai, Friedrich, 1733-1811--Correspondence.
Princeton subject headings:
Iselin, Isaak, 1728-1782--Correspondence.
Nicolai, Friedrich, 1733-1811--Correspondence.