// | Between _faces of link x2 two vertical faces are continues
// x1----x2-----x3 and two horizontal faces are continues. We set vertical faces
// | to _faces[0] and _faces[1] and horizontal faces to
// | Between _faces of link x2 two vertical faces are continues
// x1----x2-----x3 and two horizontal faces are continues. We set vertical faces
// | to _faces[0] and _faces[1] and horizontal faces to