A remark on a comparison theorem
Vincenzo Ferone, Maria Rosaria Posteraro · Communications in Partial Differential Equations · 1991
A recent comparison result ([3]) allows to get pointwise estimates for the solution of the Dirichlet problem for linear second–order elliptic equations in terms of the solution of a suitable "symmetrized" problem. In this paper we prove that equality is achieved only in the spherically symmetric situation.