Krech, Grażyna, and Eugeniusz Wachnicki. 2013. “Approximation by Some Combinations of the Poisson Integrals for Hermite and Laguerre Expansions”. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica 12 (December):21-29. https://studmath.uken.krakow.pl/article/view/13182.