“…Several aspects of the quadratic decomposition of univariate orthogonal polynomials have been already considered in the literature, see for instance, [2,4,7,11,12,[14][15][16][17][18][19] and the references therein. In [15,16] the quadratic decomposition (1.1) has been generalized for polynomial sequences non necessarily symmetric, [13] by using arbitrary polynomials of degree 2 and 1 replacing x 2 and x, respectively, in (1.1), with special attention to the quadratic transformation x 2 − 1 relating Gegenbauer and Jacobi polynomials ( [10]), or even by means of a simple cubic decomposition, as we can read for instance in [5].…”