An extension of Bochner's problem: Exceptional invariant subspaces. - David Gómez-Ullate; Niky Kamran; Robert Milson (J. Approx. Theory, 2010)

A Conjecture on Exceptional Orthogonal Polynomials. - David Gómez-Ullate; Niky Kamran; Robert Milson (Found. Comput. Math., 2013)