In this paper, we apply our recent results for fourth order functional ordinary differential equations and inequalities and obtain sufficient conditions for oscillation of all sufficiently smooth solutions of the following equation ∑ from i+j=2.4 of a_(i,j) (partial deriv)~(i+j)u(x,y)/(partial deriv)x~i(partial deriv)y~j + sum from i=1 to n of b_i(x,y)u(x-σ_i,y-τ_i)+c(x,y,u)=f(x,y), where x > 0, y > 0, a_(i,j) ∈ R, σ_i ≥ 0 and τ_i ≥ 0 are constants for all the indices. Also, we suppose that n ∈ N, b_i(x,y) ∈ C(R_+~2;R_+), {arbitrary} i = 1 - n; c(x,y,u) ∈ C(R_+~2, R;R) and f(x,y) ∈ C(R_+~2;R). In particular, we establish sufficient conditions for the distribution of zeros this equation.
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