
Keywords: تحولات Darwo; 14J70; 15A23; 33C45; 37K10; 37L60; 42C05; 46L55; Darboux transformations; Christoffel transformations; Multivariate orthogonal polynomials; Borel-Gauss factorization; Algebraic varieties; Bivariate product Legendre polynomials;