Quartet fixed point for nonlinear contraction
  The notion of coupled fixed point is introduced in by Bhaskar and Lakshmikantham in [2]. Very recently, the concept of tripled fixed point is introduced by Berinde and Borcut [1]. In this manuscript, by using the mixed g monotone mapping, some new quartet fixed point theorems are obtained. We also give some examples to support our results. 
Erdal Karapinar
math.GN