Partial regularity for quasi minimizers of perimeter: errata-corrige (Q2504732)

In [Ric. Mat. 48, Suppl., 167--186 (1999; Zbl 0943.49032)] the authors studied quasi-minimizers of perimeters and proved that the boundary of a quasi-minimizer is the union of an \((n-1)\)-dimensional \(C^{1,\alpha}\)-manifold and a closed singular set. However, it turned out that in the Theorem 4.4 the authors did not state that \(U\) was a disk. In connection with this, this note serves to give the corrected version of the theorem and to make some changes in Lemma 5.1 and Theorem 5.2.