Columbia subject headings:
Harvard subject headings:
Active galaxies--Congresses.
Quasars--Congresses
Radio sources (Astronomy)--Congresses.
Seyfert galaxies--Congresses.
Princeton subject headings:
Active galaxies--Congresses.
Quasars--Congresses.
Radio sources (Astronomy)--Congresses.
Seyfert galaxies--Congresses.