On subordination conditions for systems of minimal differential operators in the isotropic and anisotropic Sobolev spaces

The communication is devoted to the issue of characterization of elliptic (quasi-elliptic) systems of minimal differential operators using a priori estimates in the scale of isotropic (anisotropic) Sobolev spaces. A particular attention is paid to the criteria of existence of weakly coercive systems as well as to the description of wide classes of weakly coercive but not elliptic (not quasi-elliptic) systems.