  We obtain coupled coincidence and coupled common fixed point theorems for
mixed $g$-monotone nonlinear operators $F:X \times X \rightarrow X$ in
partially ordered metric spaces. Our results are generalizations of recent
coincidence point theorems due to Lakshmikantham and \' Ciri\' c
[Lakshmikantham, V., \' Ciri\' c, L., \textit{Coupled fixed point theorems for
nonlinear contractions in partially ordered metric spaces}, Nonlinear Anal.
\textbf{70} (2009), 4341-4349], of coupled fixed point theorems established by
Bhaskar and Lakshmikantham [T.G. Bhaskar, V. Lakshmikantham, \textit{Fixed
point theorems in partially ordered metric spaces and applications}, Nonlinear
Anal. \textbf{65} (2006) 1379-1393] and also include as particular cases
several related results in very recent literature.
