"Alfred Jodocus Kwak". Archived from the original on 19 October 2007. Retrieved 12 July 2017. (It's in the ‘Over Alfred’ section: ‘Toen onze … geboren, per ongeluk.’)
Wolf, Matt (11 November 1990). "Herman Van Who?". Chicago Tribune. Archived from the original on 19 October 2018. Retrieved 19 October 2010.
"Alfred Jodocus Kwak". Archived from the original on 19 October 2007. Retrieved 12 July 2017. (It's in the ‘Over Alfred’ section: ‘Toen onze … geboren, per ongeluk.’)