Erratum et Addendum zu der Arbeit: Über exzeptionelle Mengen (Q798477)

In theorem 3 of the paper reviewed above, the author claimed that if Y is a subspace of X, and you blow up X with centre Y, then, \(Y^{{\hat{\;}}}\) being the full transform of Y, then the weak negativity of \(N_ Y\) is equivalent to the one of \(N_{Y^{{\hat{\;}}}}\). The author proves here that if \(N_{Y^{{\hat{\;}}}}\) is weakly negative, then, setting \(Y_ k = the\) subspace defined by the ideal sheaf \(I^ k\), I being the ideal sheaf of Y, \(N_{Y_ k}\) is weakly negative for k large enough. - Whether the stronger result claimed in the mentioned theorem holds true is unknown to the author and to the reviewer.