  Generalizing an old result proved by P. Rao [see MR 83i:14025] for
arithmetically Cohen-Macaulay, self-linked subschemes of codimension 2 in the
projective n-space P, we give a characterization of self-linked pure subschemes
of codimension 2 in P satisfying a necessary parity condition, in
characteristic different from 2. We make use of the theory of quadratic sheaves
described in a previous paper of the authors [see MR 99h:14044].
