@article{10_21136_CMJ_1969_100917,
     author = {Vrko\v{c}, Ivo},
     title = {The class of functions fulfilling the inequality $\Vert f(x+z)-f(x)-f(y+z)+f(y) \Vert \le \Vert x-y \Vert \omega(\Vert z \Vert)$},
     journal = {Czechoslovak Mathematical Journal},
     pages = {500--514},
     publisher = {mathdoc},
     volume = {19},
     number = {3},
     year = {1969},
     doi = {10.21136/CMJ.1969.100917},
     mrnumber = {0247466},
     zbl = {0186.47602},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1969.100917/}
}