@article{GDZPPN002219646,
title = {\"Uber die Funktionalgleichung f(f(x) * f(y)) = f(x*y).},
journal = {Manuscripta mathematica},
volume = {18},
year = {1976},
pages = {371-390},
zbl = {0335.39005},
url = {http://dml.mathdoc.fr/item/GDZPPN002219646}
}
Spilker, Jürgen; Dhombres, Jean. Über die Funktionalgleichung f(f(x) * f(y)) = f(x*y).. Manuscripta mathematica, Tome 18 (1976) pp. 371-390. http://gdmltest.u-ga.fr/item/GDZPPN002219646/