“…In this paper, the second technique is considered: the singularity is introduced into the spline approximation apparatus. When constructing splines, it has long been customary to use approximation relations, since they allow one to construct spaces of splines with the required approximation properties (see [2], [12] - [16], [20] - [27]). To refine the approximation of the required functions (for example, in the finite element method) and in the compression of information flows (for example, using wavelet decompositions), a chain of embedded spline spaces on embedded grids is required.…”