Amann-Zehnder type results for p-Laplace problems
  The existence of a nontrivial solution is proved for a class of quasilinear elliptic equations involving, as principal part, either the p-Laplace operator or the operator related to the p-area functional, and a nonlinearity with p-linear growth at infinity. To this aim, Morse theory techniques are combined with critical groups estimates. 
Silvia Cingolani, Marco Degiovanni, Giuseppina Vannella
math.AP