@article{AM2_1989__37_2-3_137302,
     author = {Karl-Goswin Grosse-Erdmann},
     title = {Regularity properties of functional equations and inequalities.},
     journal = {Aequationes mathematicae},
     pages = {233--251},
     publisher = {mathdoc},
     volume = {37},
     number = {2-3},
     year = {1989},
     zbl = {0676.39007},
     url = {http://geodesic.mathdoc.fr/item/AM2_1989__37_2-3_137302/}
}