[1]  Barnett D C, Halburd R G, Korhonen R J, Morgan W. Nevanlinna theory for the q-difference operator and

meromorphic solutions of q-difference equations. Proc Roy Soc Edinburgh (Sect A), 2007, 137(3):  457--474

[2]  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(1): 105--129

[3]  Goldberg A A, Ostrovskii I V. Value Distribution of Meromorphic Functions. Transl Math Monogr, Vol 236. Providence, RI: American Mathematical Society, 2008

[4]  Gundersen G G. Meromorphic functions that share three or four values. J London Math Soc, 1979, 20(2): 457--466

[5]  Gundersen G G. Meromorphic functions that share four values. Trans Amer Math Soc, 1983, 277: 545--567

[6]  Halburd R G, Korhonen R J. Nevanlinna theory for the difference operator. Ann Acad Sci Fenn, 2006, 31(2):  463--478

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

[8]  Heittokangas J, Korhonen R, Laine I, Rieppo J. Uniqueness of meromorphic functions sharing values with their shifts. Complex Var Elliptic Equ, 2011, 56:  81--92

[9]  Heittokangas J, Korhonen R, Laine I, Rieppo J, Zhang J L. Value sharing results for shifts of meromorphic functions, and sufficient conditions for periodicity. J Math Anal Appl, 2009, 355:  352--363

[10]  Nevanlinna R. Le Th\'{e}or\`{e}me de Picard-Borel et la Th\'{e}orie des Fonctions M\'{e}romorphes. Paris:  Gauthiers-Villars, 1929

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

[12]  Li P, Yang C C. When an entire function and its linear differential polynomial share two values. Illinois J Math, 2000, 44: 349--362

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

[14]  Zhang J L, Korhonen R. On the Nevanlinna characteristic of f(qz) and its applications. J Math Anal Appl, 2010, 369:  537--544