go to Zoek [search] and type Backer, Vandersluys and variations. I found several documents relating to Paowlina or Paulina Vandersluys and her husband Jacob Backer. I also found a few documents regarding Lambertus Vandersluys and a contract to build a theater in the Kaatsban in Utrecht circa 1710. From what I can tell the Backer documents have to with rental buildings the couple owned. This site does not work with Macs and only use the Sluys to search otherwise it will not return results.