For the definition of generalized hypergeometric functions see §16.2.
See also Figure 18.21.1.
For comments on the use of the forward-difference operator , the backward-difference operator , and the central-difference operator , see §18.2(ii).
For each family only the -difference that lowers is given. See Koekoek et al. (2010, Chapter 1) for further formulas.
Koornwinder (2009) rescales and reparametrizes Racah polynomials and Wilson polynomials in such a way that they are continuous in their four parameters, provided that these parameters are nonnegative. Moreover, if one or more of the new parameters becomes zero, then the polynomial descends to a lower family in the Askey scheme.