Haruki, Shigeru, and Shin-ichi Nakagiri. 2006. “Partial Difference Equations Arising from the Cauchy-Riemann Equations”. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica 5 (June):59-76. https://studmath.uken.krakow.pl/article/view/13293.