Before revision: Balthasar van der Pol & H. Bremmer (1950) Operational calculus Cambridge University Press B. van der Pol (1950) "Heaviside's Operational Calculus" in Heaviside Centenary Volume by the Institute of Electrical Engineers R. V. Churchill (1958) Operational Mathematics McGraw-Hill J. Mikusiński (1960) Operational Calculus Elsevier A.
After revision: Balthasar van der Pol & H. Bremmer (1950) Operational calculus Cambridge University Press B. van der Pol (1950) "Heaviside's Operational Calculus" in Heaviside Centenary Volume by the Institute of Electrical Engineers R. V. Churchill (1958) Operational Mathematics McGraw-Hill J. Mikusiński (1960) Operational Calculus Elsevier