CHENG, S.S. and ZHANG, B.-G. 1994. QUALITATIVE THEORY OF PARTIAL DIFFERENCE EQUATIONS (I): OSCILLATION OF NONLINEAR PARTIAL DIFFERENCE EQUATIONS. Tamkang Journal of Mathematics. 25, 3 (Sep. 1994), 279–288. DOI:https://doi.org/10.5556/j.tkjm.25.1994.4455.