Left-definite theory with applications to orthogonal polynomials. - Andrea Bruder; Lance L. Littlejohn; Davut Tuncer; Richard Wellman (J. Comput. Appl. Math., 2010)

Differential operator for discrete Gegenbauer-Sobolev orthogonal polynomials: Eigenvalues and asymptotics. - Lance L. Littlejohn; Juan F. Mañas-Mañas; Juan J. Moreno-Balcázar; Richard Wellman (J. Approx. Theory, 2018)