Columbia subject headings:
Estonia--Biography--Congresses.
Keyserling, A. (Alexander), Graf, 1815-1891--Congresses.
Keyserling, Eduard von, 1855-1918--Congresses.
Keyserling, Hermann, Graf von, 1880-1946--Congresses.
Harvard subject headings:
Estonia--Biography--Congresses.
Keyserling, A. (Alexander), graf, 1815-1891--Congresses.
Keyserling, Eduard von, 1855-1918--Congresses.
Keyserling, Hermann, Graf von, 1880-1946--Congresses.
Princeton subject headings:
Estonia--Biography--Congresses.
Keyserling, A. (Alexander), Graf, 1815-1891--Congresses.
Keyserling, Eduard von, 1855-1918--Congresses.
Keyserling, Hermann, Graf von, 1880-1946--Congresses.