Abstract
We show that the following system of difference equations
2000 Mathematics Subject Classification::
Acknowledgements
The second author was supported by the Grant P201/10/1032 of the Czech Grant Agency (Prague). The fourth author was supported by the grant FEKT-S-11-2-921 of Faculty of Electrical Engineering. This paper was also supported by the Serbian Ministry of Science projects III 41025, III 44006 and OI 171007.