The aim of this work is to establish the existence of infinitely many solutions to gradient elliptic system problem, placing only conditions on a potential function , associated to the problem, which is assumed to have an oscillatory behaviour at infinity. The method used in this paper is a shooting technique combined with an elementary variational argument. We are concerned with the existence of upper and lower solutions in the sense of Hernández.
Abdelaziz Ahammou. "A multiplicity result for a quasilinear gradient elliptic system." J. Appl. Math. 1 (3) 91 - 106, 16 September 2001. https://doi.org/10.1155/S1110757X01000274