  T. Szemberg proposed in 2001 a generalization to arbitrary varieties of M.
Nagata's 1959 open conjecture, which claims that the Seshadri constant of r>9
very general points of the projective plane is maximal. Here we prove that
Nagata's original conjecture implies Szemberg's for all smooth surfaces X with
an ample divisor L generating its Neron-Severi group and such that L^2 is a
square. More generally, we prove that the (n-1)-dimensional Seshadri constant
of an ample divisor L on a projective variety X of dimension n at r very
general points is bounded below by the product of the (n-1)-dimensional
Seshadri constant of at a very general point times the (n-1)-dimensional
Seshadri constant of the hyperplane on projective n-space at r very general
points.
