Type Theory and Homotopy Theory. Staff Colloquium, Dept. of Mathematics, UU, March 17, 2011.

Synthetic Nonstandard Arithmetic.Kolloquium des Fachbereichs Mathematik der TU Darmstadt, May 11, 2011.

Local Operators in the Effective Topos. "Proofs and Programs", Luminy, February 16, 2012 (invited talk).

Classical Realizability. Cambridge Category Seminar, March 6, 2012 (invited talk).

More about Geometric Morphisms between Realizability Toposes. Category Theory meeting (CT14), Cambridge, July 2, 2014 (invited plenary lecture).

Intuitionism, Generalized Computability and Effective Operations, Heyting Day, February 27, 2015 (Lectures in honour of the 75th birthdays of Anne Troelstra and Dick de Jongh).

Concrete Models for Classical Realizability, Utrecht Workshop on Proof Theory, April 16, 2015.

Classical and Relative Realizability, 100th PSSL, Cambridge, May 21, 2016.

Topological Models of Computability, Nederlands Mathematisch Congres 53, Utrecht, April 11, 2017.

Partial Combinatory Algebras - Variations on a Topos-theoretic Theme, Wisconsin Logic Seminar, November 17, 2020.

Partial Combinatory Algebras - Variations on a Topos-theoretic Theme, UGC Seminar, April 4, 2021.

Everything is Relative -- Some Remembrances of Pieter Hofstra's Personality and Work, October Fest, Ottawa, October 29,2022.

Partial Combinatory Algebras -- Between realizability and oracle computations, Tulips seminar, March 16, 2023.

Keuze-Axioma en filosofische vragen over de Wiskunde. Voordracht voor *Communiceren in de Wiskunde*, 3 april 2012.

Onvolledigheidsstellingen van Gödel. A-eskwadraat symposium, 11 december 2014.

Algoritmen, abstract bezien. Gastcollege bij Programmeren in de Wiskunde, 25 juni 2015.

Observations, Truth and Logic. Talk at student symposium Axioma, Groningen, May 9, 2018.

Verzamelingen, eindig en oneindig. Cursus U-Talent masterclass, oktober 2019.

Back to base.