On subordination conditions for systems of minimal di erential operators

In this paper, we provide a review of results on a priori estimates for systems of minimal differential operators in the scale of spaces \(L^p(\Omega),\) where \(p\in[1,\infty].\) We present results on the characterization of elliptic and \(l\)-quasielliptic systems using a priori estimates in isotropic and anisotropic Sobolev spaces \(W_{p,0}^l(\mathbb
R^n),\) \(p\in[1,\infty].\) For a given set \(l=(l_1,\dots,l_n)\in\mathbb
N^n\) we prove criteria for the existence of \(l\)-quasielliptic and weakly coercive systems and indicate wide classes of weakly coercive in \(W_{p,0}^l(\mathbb
R^n),\) \(p\in[1,\infty],\) nonelliptic, and nonquasielliptic systems. In addition, we describe linear spaces of operators that are subordinate in the \(L^\infty(\mathbb R^n)\)-norm to the tensor product of two elliptic differential polynomials.