Columbia subject headings:
Galaxies--Evolution--Congresses.
Hubble, Edwin, 1889-1953--Congresses.
Harvard subject headings:
Galaxies--Evolution--Congresses
Hubble, Edwin, 1889-1953
Hubble, Edwin, 1889-1953.
Princeton subject headings:
Galaxies--Evolution--Congresses.
Hubble, Edwin, 1889-1953--Congresses.