On the Danilov-Gizatullin Isomorphism Theorem
Résumé
A Danilov-Gizatullin surface is a normal affine surface V=F d\S, which is a complement to an ample section S in a Hirzebruch surface Fd. By a surprising result due to Danilov and Gizatullin, [DaGi] V depends only on n=S^2 of S and neither on d nor on S. In this note we provide a new and simple proof of this Isomorphism Theorem.