Columbia subject headings:
Popper, Karl R. (Karl Raimund), 1902-1994.
Rationalism.
Harvard subject headings:
Popper, Karl R. (Karl Raimund), 1902-1994--Congresses.
Rationalism--History--20th century--Congresses.
Princeton subject headings:
Popper, Karl R. (Karl Raimund), 1902-1994--Congresses.
Rationalism--History--20th century--Congresses.