Stratification IR³₊. The whole space is split into 7 subsets by the cone , the planes drawn through the ribs of and the coordinate axes, and the coordinate planes. In the set I (º ) the problem (1) is equivalent to the problem (4) with J={1; 2; 3}, in II with J={1; 2}, in III with J={1; 3}, in IV with J={2; 3}, in V with J={1}, in VI with J={2} and in VII with J={3}.