Let X be an integral projective variety of codimension two, degree d and
dimension r and Y be its general hyperplane section. The problem of lifting
generators of minimal degree σ from the homogeneous ideal of Y to the
homogeneous ideal of X is studied. A conjecture is given in terms of d, r
and σ; it is proved in the cases r=1,2,3. A description is given of
linear systems on smooth plane curves whose dimension is almost maximal.Comment: 19 pages, AmS-TeX 2.1, report