1. Allegretto, W., Barabanova, A.: Positivity of solutions of elliptic equations with nonlocal terms. Proc. R. Soc. Edinb. Sect. A 126, 643–663 (1996)
2. Belloni, M., Kawohl, B.: A symmetry problem related to Wirtinger’s and Poincaré’s inequality. J. Differ. Equ. 156(1), 211–218 (1999)
3. Brandolini, B., Della Pietra, F., Nitsch, C., Trombetti, C.: Symmetry breaking in a constrained Cheeger type isoperimetric inequality. ESAIM Control Optim. Calc. Var. 21(2), 359-371 (2015)
4. Brandolini, B., Freitas, P., Nitsch, C., Trombetti, C.: Sharp estimates and saturation phenomena for a nonlocal eigenvalue problem. Adv. Math. 228(4), 2352–2365 (2011)
5. Brock, F., Croce, G., Guibé, O., Mercaldo, A.: Symmetry and asymmetry of minimizers of a class of noncoercive functionals.
arXiv:1601.07327
(2016)