Consider the first order
linear difference equation
where Δu(k) = u(k + 1) − u(k), p : N → ℝ+, τ : N → N, τ(k) ≤ k − 2 and
limk→+∞τ(k) = +∞. Optimal conditions for the oscillation of all proper solutions of
this equation are established. The results lead to a sharp oscillation condition,
when k − τ(k) → +∞ as k → +∞. Examples illustrating the results are
given.