3Zhang Shisheng, Guo Weiping. On the existence and uniqueness theorems of solutions for the systems of mixed monotone operator equations with applications, [J]. Appliet. A Journal of Chinese Universties(SerB), 1993,8:11 - 14.
4Guo Dajun, Lakshmikantham v. Coupled fixed points of nonlinear operators with application[ J ]. Nonlinear Anal, 1987, ( 11 ) :623 - 632.