Crstici, Borislav, and Mihai Neagu. “Extensions of Some Finite Difference Equations for the Case of Distributions”. Anal. Numér. Théor. Approx., vol. 11, no. 1, Aug. 1982, pp. 49-57, https://ictp.acad.ro/jnaat/journal/article/view/1982-vol11-nos1-2-art6.