WEBThe Brauer Group. The Brauer group of a field K may be defined to be the group of similarity classes of central simple algebras over K or, equivalently, the cohomology group. H2.Gal.Ksep=K/;Ksep/ D H2..SpecK/et;Gm/: Both of these definitions generalize to schemes, but they may give different groups. The first group, that of similarity classes ...