On the first twisted Dirichlet eigenvalue (Q1769132)

\textit{L. Barbosa} and \textit{P. Bérard} [J. Math. Pures Appl., IX. Sér. 79, No. 5, 427--450 (2000; Zbl 0958.58006)] stated the twisted eigenvalue problem and presented some basic properties. In the paper under review, the authors prove an isoparametric inequality for the twisted Dirichlet eigenvalue. More precisely, they show that in the Euclidean case this eigenvalue is minimized by the union of two equal balls. This uses a result on the ratio of the first zero of consecutive Bessel functions. In the last section, some remarks and open problems are stated.