[1]    K. Hila, Filters in ordered G-semigroups, Rocky Mountain J. Math. 41(1) (2011), 189-203.

[2]    N. Kehayopulu and M. Tsingelis, On the decomposition of prime ideals of ordered G-semigroups into their -classes, Semigroup Forum 47 (1993), 393-395.

[3]    M. Petrich, Introduction to Semigroups, Merrill, Columbus, 1973.

[4]    M. K. Sen and N. K. Saha, On G-semigroup I, Bull. Cal. Math. Soc. 78 (1986), 180-186.

[5]    M. K. Sen and A. Seth, On po-G-semigroups, Bull. Cal. Math. Soc. 85(5) (1993), 445-450.