[1] Paul Erdös, William Feller, and Harry Pollard:
A property of power series with positive coefficients.
Bull. Amer. Math. Soc. 55 (1949), 201-204.

[2] Harry Pollard and Harold Widom:
Inversion of an integral transform.
Proc. Amer. Math. Soc. 9 (1958), 598-602.

[3] Albrecht Böttcher and Harold Widom:
Two remarks on spectral approximations for Wiener-Hopf operators.
J. Integral Equations Appl. 6 (1994), 31-36.