The well-known and beautiful
result of J. L. Walsh, on the overconvergence of sequences of differences of
polynomials interpolating a function f(z) analytic in |z| < ρ (but having a singularity
on |z| = ρ), where 1 < ρ < ∞, has been recently extended in a new direction by T. J.
Rivlin. We give here three new extensions of Rivlin’s result, which include Hermite
and Birkhoff interpolation.