@article{CMUC_2008__49_4_a4,
     author = {Rempulska, Lucyna and Tomczak, Karolina},
     title = {On approximation of functions by certain operators preserving $x^2$},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {579--593},
     publisher = {mathdoc},
     volume = {49},
     number = {4},
     year = {2008},
     mrnumber = {2493939},
     zbl = {1212.41054},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_2008__49_4_a4/}
}