R. Rao, K., P. R. Swamy, S. Sadik, and E. Ramudu. “Suzuki Type Common Fixed Point Theorem For Four Maps Using α - Admissible Functions In Partial Ordered Complex Valued Metric Spaces”. Journal of Progressive Research in Mathematics, Vol. 7, no. 1, Mar. 2016, pp. 928-39, http://scitecresearch.com/journals/index.php/jprm/article/view/676.