...elliptic and parabolic problems, pp. 156-163, Pitman Res. Notes Math. Series, 266 Longman (1992). 18. Kazdan, JL and Kramer, RJ Invariant criteria for existence of solutions to quasilinear elliptic equations, Commun. Pure Applied Math. ,31, 619-645 (1989). 1 9. Keller, JB Electrohydrodynamics...