Columbia subject headings:
Harvard subject headings:
Hempel, Carl G. (Carl Gustav), 1905-1997--Congresses.
Popper, Karl R. (Karl Raimund), 1902-1994--Congresses.
Princeton subject headings:
Hempel, Carl G. (Carl Gustav), 1905-1997--Congresses.
Knowledge, Theory of--Congresses.
Popper, Sir Karl Raimund, 1902---Knowledge, Theory of--Congresses.