1. B. Aloui, F. Marcellán and R. Sfaxi, Classical orthogonal polynomials with respect to a lowering operator generalizing the Laguerre operator, Integral Transforms Spec. Funct., 24 (2013), 636–648.
2. B. Aloui and W. Chammam, Classical orthogonal polynomials via a second-order linear differential operators, Indian J. Pure Appl. Math. (2020) (to appear).
3. S. Bochner, Über Sturm-Liouvillesche Polynomsysteme, Math Z., 29 (1929), 730–736.
4. E. Buendia, J. S. Dehesa and F. J. Galvez, The distribution of zeros of the polynomial eigenfunctions of ordinary differential operators of arbitrary order, in: Orthogonal Polynomials and their Applications, Alfaro, M. et al. (eds.), Lecture Notes in Mathematics, vol. 1329, Springer (1986), pp. 222–235.
5. K. M. Case, Sum rules for zeros of polynomials. I, II, J. Math. Phys., 21 (1980), 702–708, 709–714.