Oscillation criteria for first-order systems of linear difference equations

In this article, we obtain conditions for the oscillation of vector solutions to the first-order systems of linear difference equations $$displaylines{ x(n+1)=a(n)x+b(n)y cr y(n+1)=c(n)x+d(n)y }$$ and $$displaylines{ x(n+1)=a(n)x+b(n)y+f_1(n) cr y(n+1)=c(n)x+d(n)y+f_2(n) }$$ where $a(n), b(n), c(n), d(n) $ and $f_i(n), i=1, 2$ are real valued functions defined for $n geq 0$.