Differential-geometric structures defining higher order contact transformations

The paper is devoted to the study of differential-geometric structures generated by Lie–Bäcklund transformations (or, what is the same, higher order contact transformations), which are a special case of diffeomorphisms between two manifolds of holonomic jets of sections. We study the structure of the fundamental object of a second order contact diffeomorphism (2-diffeomorphism). We also consider the case when a 2-diffeomorphism is given by explicit equations connecting local coordinates of 2-jet manifolds and establish conditions under which 2-diffeomorphisms defined by explicit equations are contact diffeomorphisms.