@article{AM2_1982__25_136966,
     author = {Detlef Gronau},
     title = {Two iterative functional equations for power series.},
     journal = {Aequationes mathematicae},
     pages = {233--246},
     publisher = {mathdoc},
     volume = {25},
     year = {1982},
     zbl = {0526.39009},
     url = {http://geodesic.mathdoc.fr/item/AM2_1982__25_136966/}
}