@article{AM2_1992__43_1_137467,
     author = {Zsolt P\'ales},
     title = {On reduction of linear two variable functional equations to differential equations without substitutions.},
     journal = {Aequationes mathematicae},
     pages = {236--247},
     year = {1992},
     volume = {43},
     number = {1},
     zbl = {0755.39005},
     url = {http://geodesic.mathdoc.fr/item/AM2_1992__43_1_137467/}
}