EN
We consider the Darboux problem for a functional differential equation:
$(∂²u)/(∂x∂y) (x,y) = f(x,y,u_{(x,y)},u(x,y),∂u/∂x (x,y),∂u/∂y (x,y))$ a.e. in [0,a]×[0,b],
u(x,y) = ψ(x,y) on [-a₀,a]×[-b₀,b]∖(0,a]×(0,b],
where the function $u_{(x,y)}:[-a₀,0]×[-b₀,0] → ℝ^{k}$ is defined by $u_{(x,y)}(s,t) = u({s+x},{t+y})$ for (s,t) ∈ [-a₀,0]×[-b₀,0]. We give a few theorems about weak and strong inequalities for this problem. We also discuss the case where the right-hand side of the differential equation is linear.