This note contains a new
proof of a theorem of Gang Xiao saying that the bicanonical map of a surface S of
general type is generically finite if and only if p2(S) > 2. Such properties are also
studied for adjoint linear systems |KS+ L|, where L is any divisor with
h0(S,𝒪S(L)) ≥ 2.
Keywords
bicanonical map, algebraic surface, adjoint linear system