Portrait by Tine
Blankenstein, 2002 (click in order to enhance); picture 10 years later (Luminy, february 2012); Gil Cavalcanti's view (november 2013); official photograph Mathematical Institute (March 2022).

This is the Mathematics Football Team 2005 (University Competition; 9th place).

And this is the beautiful building I work in.

My e-mail address is

My office phone number is

My Ph.D. thesis.

A few downloadable recent papers of mine.

Here are some slides of recent talks.

A lot of my work has to do with Realizability. Here is a page with recent papers on Realizability and related subjects.

I have written a book on Realizability: *Realizability - An Introduction to its Categorical Side*, which has appeared March 2008 as Studies in Logic 152:

Here are Preface, Introduction and table of contents.

Here is a review of the book by Colin McLarty.

Here is the review of the book by Peter T. Johnstone, Bull. of Symbolic Logic 16 (3), September 2010, pp.407-409.

The basic Logic lecture course *Sets, Models and Proofs* (joint work with Ieke Moerdijk) appeared with Springer in December 2018. See this review on MathSciNet and this review on the MAA web page.

I am *not* an intuitionist.

*``It may be true that sadism is an important element in teaching, but it is better if it is at least
partly sublimated and not openly encouraged by being flaunted before an audience''* - Charles Rosen,
*Piano Notes*

My teaching page, with lecture course materials.

Ein *Urteil* behauptet einen Sachverhalt; besteht dieser Sachverhalt, so ist das Urteil wahr, andernfalls unwahr.

Hermann Weyl, Das Kontinuum

Der Mensch kann denken, insofern er die Möglichkeit dazu hat.

Martin Heidegger, Was heisst Denken?

To every rule there is an exception. And the only exception to the rule, that to every rule there is an exception, is the rule that to every rule there is an exception.

Het aller-absoluutste niets

is van een niet-bestaande fiets

het niet met iets gevuld zijn van de

al evenmin bestaande banden.

Zou het dan gek zijn, vroeg een hond,

als daar geen fietspomp voor bestond?

K. Stip, *Op een hond*

Oh, there are *signs* of life in the university, I tell W. It *seems* that it's alive. But that life is the life of maggots, I tell W., devouring the substance of the university from the inside, living on its rotting.

The corpse of the university is a breeding ground, I tell W. The corpse is where Capital comes to lay its eggs. The university is that rotten place where Capital deposits its eggs...

Lars Iyer, *Exodus*

It is not necessary that you leave the house. Stay at your table and hearken. Don't even hearken, just wait. Don't even wait, be perfectly still and alone. There the world will offer herself to be unmasked, she must, she will writhe ecstatically before you.

Kafka, *Aphorismen-Zettelbuch 1920* (my translation)

Here are some memories of Anne Troelstra, who died March 2019.

Here is how I remember Pieter Hofstra, who died May 1, 2022.

Here is a link to my close friend and colleague Kuba Wschodni.

Hier is een bijdrage aan de discussie rond Maarten van Buuren's *De afrekening*.

Hier is een bijdrage aan de discussie rond Dodenherdenking.

Hier is een Open brief aan Beatrix.

Here is a comment on Timothy Snyder's "Black Earth".

I wish you well.