@article{AM2_1989__38_1_137316,
     author = {Gy. Petruska},
     title = {On a functional equation with retarded mean.},
     journal = {Aequationes mathematicae},
     pages = {66--72},
     publisher = {mathdoc},
     volume = {38},
     number = {1},
     year = {1989},
     zbl = {0679.39007},
     url = {http://geodesic.mathdoc.fr/item/AM2_1989__38_1_137316/}
}