Columbia subject headings:
Frege, Gottlob, 1848-1925.
Popper, Karl R. (Karl Raimund), 1902-1994.
Harvard subject headings:
Frege, Gottlob, 1848-1925.
Popper, Karl R. (Karl Raimund), 1902-1994.
Princeton subject headings:
Frege, Gottlob, 1848-1925.
Popper, Karl R. (Karl Raimund), 1902-1994.