Herlyn, I., and U. Vogel. “Familienfrauen Am Ende Ihrer Aktiven Mutterphase: Family Women at the End of Their Motherhood Phase”. Journal of Family Research, vol. 6, no. 1/2, Sept. 1994, pp. p. 6-15, https://ubp.uni-bamberg.de/jfr/index.php/jfr/article/view/585.