  Our main theorem characterizes the complete intersections of codimension 2 in
a projective space of dimension 3 or more over an algebraically closed field of
characteristic 0 as the subcanonical and self-linked subschemes. In order to
prove this theorem, we'll prove the Gherardelli linkage theorem, which asserts
that a partial intersection of two hypersurfaces is subcanonical if and only if
its residual intersection is, scheme-theoretically, the intersection of the two
hypersurfaces with a third.
