  We consider a boundary value problem for a general second order linear
equation in a perforated domain. The perforation is made by small cavities, a
minimal distance between the cavities is also small. We impose minimal natural
geometric conditions on the shapes of the cavities and no conditions on their
distribution in the domain. On the boundaries of the cavities a nonlinear Robin
condition is imposed. The sizes of the cavities and the minimal distance
between them are supposed to satisfy a certain simple condition ensuring that
under the homogenization the cavities disappear and we obtain a similar problem
in a non-perforated domain. Our main results state the convergence of the
solution of the perturbed problem to that of the homogenized one in $W_2^1$-
and $L_2$-norms uniformly in $L_2$-norm of the right hand side in the equation
and provide the estimates for the convergence rates. We also discuss the order
sharpness of these estimates.
