Krutitskii, P. A., and N. C. Krutitskaya. “The Harmonic Dirichlet Problem in a Planar Domain With Cracks”. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, vol. 7, Nov. 2008, pp. 113-2, https://studmath.uken.krakow.pl/article/view/13273.