Asymptotics of a section by a plane of the sub-Riemannian sphere on the Engel group near abnormal trajectory

In this paper we compute an asymptotics of the curve that is the intersection of the unit sub-Riemannian sphere on the Engel group with the subspace $\{x=z=0\}$ near the abnormal trajectory. It follows from the asymptotics that this curve is not analytic at the point $(1, 0, 0, 0)$. (In Russian).