Let fsβ:XsββP2 be the blowing-up of s distinct points and
E a vector bundle on Xsβ. Here we give a cohomological criterio which is
equivalent to Eβ fsββ(A) with A a direct sum of line bundles. We
also some cohomological characterizations of very particular rank 2 vector
bundles on P2.Comment: 6 pages, no figure