A boundary value problem for higher order elliptic equations in many connected domain on the plane

For the elliptic equation of $2l$th order with constant (and leading) coefficients boundary value a problem with normal derivatives of the $(k_j-1)-$order, $j=1,\ldots,l$ considered. Here $1\le k_1 <\ldots< k_l\le 2l$. When $k_j=j$ it moves to the Dirichlet problem, and when $k_j = j + 1$ it corresponds to the Neumann problem. The sufficient condition of the Fredholm problem and index formula are given.