1. Alt, H.W., Caffarelli, L.A.: Existence and regularity for a minimum problem with free boundary. J. Reine Angew. Math. 325, 105–144 (1981)
2. Alt, H.W., Caffarelli, L.A., Friedman, A.: Variational problems with two phases and their free boundaries. Trans. Am. Math. Soc. 282(2), 431–461 (1984)
3. Ambrosetti, A., Rabinowitz, P.H.: Dual variational methods in critical point theory and applications. J. Funct. Anal. 14, 349–381 (1973)
4. Berestycki, H., Caffarelli, L.A., Nirenberg, L.: Uniform estimates for regularization of free boundary problems. In: Analysis and Partial Differential Equations, Volume 122 of Lecture Notes in Pure and Applied Mathematics, pp. 567–619. Dekker, New York (1990)
5. Bonforte, M., Grillo, G., Vazquezo, J.L.: Quantitative bounds for subcritical semilinear elliptic equations. In: Recent Trends in Nonlinear Partial Differential Equations. II. Stationary Problems, Volume 595 of Contemporary Mathematics, pp. 63–89. American Mathematical Society, Providence, RI (2013)