[1] Hayman W K. Meromorphic Functions. Oxford: Clarendon Press, 1964

[2] Laine I. Nevanlinna Theory and Complex Differential Equations. Berlin: Walter de Gruyter, 1993

[3] Nevanlinna R. Analytic Functions. Berlin: Springer-Verlag, 1970

[4] Yang C C, Yi H X. Uniqueness Theory of Meromorphic Functions. Dordrecht: Kluwer Academic Publishers Group, 2003

[5] Bergweiler W, Ishizaki K, Yanagihara N. Meromorphic solutions of some functonal equations. Methods Appl Anal,  1998, 5(3): 248--258 (Correction: Methods Appl Anal, 1999, 6(4): 617--618)

[6] Bergweiler W, Langley J K. Zeros of differences of meromorphic functions. Math Proc Cambridge Phil Soc,  2007,
142: 133--147

[7] Chen Z X, Huang Z B, Zheng X M. On properties of difference polynomials. Acta Math Scientia,  2011, 31B(2):
627--633

[8] Chiang Y M, Feng S J. On the nevanlinna characteristic of f(z+η) and difference equations in the complex plane. Ramanujan J, 2008, 16: 105--129

[9] Halburd R G, Korhonen R J. Difference analogue of the lemma on the logarithmic derivative with applications to difference equations. J Math Anal Appl, 2006, 314: 477--487

[10] Halburd R G, Korhonen R J. Meromorphic solutions of difference equations, integrability and the discrete painlev\'{e}
equations. J Phys A, 2007, 40: 1--38

[11] Heittokangas J, et al. Complex difference equations of malmquist type. Comput Methods Funct Theory,  2001, 1(1): 27--39

[12] Korhonen R. An extension of Picard's theorem for meromorphic functions of small hyper-order. J Math Anal Appl, 2009, 357: 244--253

[13] Laine I, Yang C C. Clunie theorems for difference and q-difference polynomials. J London Math Soc, 2007, 76: 556--566

[14] Laine I, Yang C C. Value distribution of difference polynomials. Proc Japan Acad (Ser A),  2007, 83: 148--151

[15] Liu K, Qi X G. Meromorphic solutions of q-shift difference equations. Ann Polon Math, 2011, 101(3): 215--225

[16] Zheng X M, Tu J. Growth of meromorphic solutions of linear difference equations. J Math Anal Appl, 2011, 384(2): 349--356

[17] Zheng X M, Chen Z X. On properties of q-difference equations. Acta Math Scientia, 2012, 32B(2): 724--734

[18] Hayman W K. Picard values of meromorphic functions and their derivatives. Ann of Math, 1959, 70(2): 9--42

[19] Hayman W K. On the characteristic of functions meromorphic in the plane and of their integrals. Proc London Math Soc, 1965, 14A(3):  93--128