1. Ambrosio, L., Fusco, N., Pallara, D.: Functions of bounded variation and free discontinuity problems. Oxford Mathematical Monographs, xviii+434 pp. Oxford University Press, New York (2000)
2. Bellettini, G., Dacorogna, B., Fusco, G., Leonetti, F.: Qualitative properties of Lipschitz solutions of eikonal type systems. Adv. Math. Sci. Appl. 16(1), 259–274 (2006)
3. Cardaliaguet, P., Dacorogna, B., Gangbo, W., Georgy, N.: Geometric restrictions for the existence of viscosity solutions. Ann. Inst. H. Poincaré Anal. Non Linéaire 16(2), 189–220 (1999)
4. Cellina, A.: On minima of a functional of the gradient: necessary conditions. Nonlinear Anal. 20(4), 337–341 (1993)
5. Cellina, A.: On minima of a functional of the gradient: sufficient conditions. Nonlinear Anal. 20(4), 343–347 (1993)