On the uniqueness and simplicity of the principal eigenvalue. (English) Zbl 1225.35159
Atti Accad. Naz. Lincei, Cl. Sci. Fis. Mat. Nat., IX. Ser., Rend. Lincei, Mat. Appl. 16, No. 2, 133-142 (2005).
MSC:
35P30