Characterization of classical orthogonal polynomials in two variables

For a family of polynomials in two variables, orthogonal with respect to a weight function, we prove under some conditions, equivalence between: the Matrix Pearson equation of the weight, the second order linear partial differential equation, the orthogonality of the gradients, the Matrix Rodrigues formula involving tensor product of Matrices, and the so-called first structure relation. We then propose a definition of classical orthogonal polynomials in two variables.