A critical point theorem via the Ekeland variational principle

The aim of this paper is to establish the existence of a local minimum for a continuously Gateaux differentiable function, possibly unbounded from below, without requiring any weak continuity assumption. Several special cases are also emphasized. Moreover, a novel definition of Palais-Smale condition, which is more general than the usual one, is presented and a mountain pass theorem is pointed out. As a consequence, multiple critical points theorems are then established. Finally, as an example of applications, an elliptic Dirichlet problem with critical exponent is investigated. (C) 2011 Elsevier Ltd. All rights reserved.