1. A symmetry problem in potential theory;Serrin;Arch. Ration. Mech. Anal.,1971
2. On overdetermined boundary value problems for the biharmonic operator;Payne;J. Math. Anal. Appl.,1994
3. On some second order and fourth order elliptic overdetermined problems;Philippin;Z. Angew. Math. Phys.,1995
4. Maximum Principles in Differential Equations;Protter,1967
5. Remark on the preceding paper of Serrin;Weinberger;Arch. Ration. Mech. Anal.,1971