"Dhr. E.J. ter Keurs" [Mr. E.J. ter Keurs] (in Dutch). Gemeente Tytsjerksteradiel. Archived from the original on 3 October 2013. Retrieved 30 September 2013.
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"Dhr. E.J. ter Keurs" [Mr. E.J. ter Keurs] (in Dutch). Gemeente Tytsjerksteradiel. Archived from the original on 3 October 2013. Retrieved 30 September 2013.