The Genlias Monitor is a free service for genealogists who automatically want to receive new additions to Genlias, the database of the Dutch national archives, to complement their genealogy.
What is a patronymic? - from the Genlias FAQ
A patronymic is a name based upon that of the person's father. So a child called Harm whose father's forename was Jan would often be called Harm Jans. The suffix "Jans" is the patronymic. If you know the patronymic of the person you are looking for, enter it under "First person". The "Second person" field is for the name of another person mentioned on a certificate or whose name you know.