It is stated that this article does not cite any references or sources.
What do the Wikipedia members expect here? Just the names of several dutch biographies, like those of Jan Drentje, or the edition of his letters (by G.J. Hooykaas). It is no problem to do so, but what will it add for the english speaking community? Those able to read Dutch will consult the dutch wiki page, and the references cited there.
Please clarify, and I will be more than happy to add anything you think will enhance the reliability of this article. Donjanssen (talk) 18:03, 10 November 2008 (UTC)