1. Gibbs, J.E., Walsh Functions as Solutions of a Logical Differential Equation, National Physical Lab., Teddingon, England, DES Report, No. 1, 1969.
2. Gibbs, J.E., Simpson, J., Differentiation on Finite Abelian Groups, National Physical Lab. Teddington, England, DES Rept, No. 14, 1974.
3. Butzer, P.L., Wagner, H.J., Walsh-Fourier Series and the Concept of a Derivative, Applicable Analysis, Vol. 3, pp. 29–46, 1973.
4. Onneweer, C.W., Fractional Differentiation on the Group of Integers of a p-adic or p-series field. Anal. Math., Vol. 3, pp. 119–130, 1977.
5. Moraga, C., Introduction to Linear p-adic Invariant Systems, Cybernetics and Systems Research, Vol. 2, pp. 121–124, Ed., R. Trappl, Vienna: Electronic Science Publ., 1984.