[en] The problem of existence of the discrete energy level in a zeroarea potential field is investigated. It is shown that the (A, K) plane is devided into three regions separated by parabolas in the case of carmonic pulse. In the region I, to the left of the critical region 2, the soliton formation is always possible. In region 3, to the right of the critical one, the soliton formation is forbidden. The same result is obtained for the Gaussian pulse but the boundary curves are described by the cubic law. The comparison with numerical experiment data is made. The basic parameters of numerical integration of the Kortewg-De Vries equation are presented