EN
Consider a nonlinear differential-functional equation
(1) Au + f(x,u(x),u) = 0
where
$Au := ∑_{i,j=1}^m a_{ij}(x) (∂²u)/(∂x_i ∂x_j)$,
$x=(x_1,...,x_m) ∈ G ⊂ ℝ^m$, G is a bounded domain with $C^{2+α}$ (0 < α < 1) boundary, the operator A is strongly uniformly elliptic in G and u is a real $L^p(G̅)$ function.
For the equation (1) we consider the Dirichlet problem with the boundary condition
(2) u(x) = h(x) for x∈ ∂G.
We use Chaplygin's method [5] to prove that problem (1), (2) has at least one regular solution in a suitable class of functions.
Using the method of upper and lower functions, coupled with the monotone iterative technique, H. Amman [3], D. H. Sattinger [13] (see also O. Diekmann and N. M. Temme [6], G. S. Ladde, V. Lakshmikantham, A. S. Vatsala [8], J. Smoller [15]) and I. P. Mysovskikh [11] obtained similar results for nonlinear differential equations of elliptic type.
A special case of (1) is the integro-differential equation
$Au + f(x,u(x), ∫_G u(x)dx) = 0$.
Interesting results about existence and uniqueness of solutions for this equation were obtained by H. Ugowski [17].