Giving talks or lectures in courses, conferences, symposia, is next to books and articles in journals instrumental for the distribution of our progress and insights. Through the past 70 years the means of presentation changed considerably. The generation of this author (now age 77) grew up with blackboards and white or colored chalk crayons, later the green boards, still later the whiteboards. I fantasize about lectures some millennia ago, in a cave with a lecturer drawing animals to hunt. After the blackboard many of us became familiar with the epi(dia)scope with its transparencies. Until the beamer appeared, and Powerpoint became prevalent, except for some Mac afficianados and aficianadas who use Keynote.  Including this site’s author. Now we are waiting for VR glasses to wear during lectures!

Bertinoro 2005

The  Workshop Algebraic Process Calculi: The First Twenty Five Years and Beyond was held in the period August 1-5, 2005, at the University Residential Centre of Bertinoro, Forlì, Italy. The workshop proceedings are available as PDF, BRICS Notes Series ISSN 0909-3206 NS-05-3, eds. Luca Aceto and Andrew Gordon.

The following link is for the lecture of Jan Willem Klop in this workshop, at the beautiful place of Bertinoro, in the company of many process algebra friends and colleagues, as on some of the photos.

Classifying streams-v2





A talk give at the 60th anniversary of CWI, Amsterdamm 12 december 2006 , with many persons having shaped this 60 year history, and some explanation of process algebra, one of the subjects that were worked on at CWI.

Defining the undefined Madeira 30p


Dubrovnik 2006 LICS Tutorial

LICS 2006 was held in the beautiful coastal city of Dubrovnik in Croatia. Participation from the Vrije Universiteit Amsterdam consisted of a presentation of recent work by Clemens Grabmayer, and an invited three hour tutorial on Term Rewriting by Joerg Endrullis and Jan Willem Klop, reachable in the LICS archives and also included here.






This lecture ‘New Fixed Point Combinators from Old’ was in honour of Henk Barendregt turning 60, on December 17, 2007, in Nijmegen.

The first part contains many pictures and sentimental memorie to the years we were almost neighbbours in Utrecht, around 1976, including some memorable joint visits to conferences in La Chatre France, 1978 and Ustica Italy, 1985, Tsukuba, Japan 1989.

The second part of the talk was devoted to construct families of new fixed point combinators, via an excursion to infinitary lambda calculus.


This lecture ‘Clocks, black holes and white holes in the lambda calculus’ was part of the one day symposium Symposium for Henk Barendregt, Detachment: mathematics and meditation, October 1, 2015, Radboud Universiteit Nijmegen. The contents are:

  1. An inkling of lambda calculus and combinatory logic
  2. Black holes in the lambda calculus: Henk’s notion of unsolvables
  3. Fixed point combinators
  4. Clocks in the lambda calculus
  5. Rivers of knowledge 






Sequentiality in lambda calculus and CL, University of Tsukuba, March 27, 1998.

This lecture is about joint work with Inge Bethke, Richard Kennaway, Ronan Sleep, Fer-Jan de Vries, concerning the syntactic definition of the three main semantics of lambda calculus, to wit via Bohm Trees, via Levy-longo Trees, and via Berarducci Trees. An application gives Berry’s theorem about the sequential nature of the lambda calculus.

This travel to Japan was one in a most fruitful series, to our Japanese friends and colleagues. One of these travels was made in the company of my family, Marianne and daughter Maartje, here in front of the magnificent Golden Temple in Kyoto.

Taart voor Hans Zantema

9 September 2022 Eindhoven, talk initially in Dutch, Hoe  verdelen we de taart? (How to distribute the pie?) On the occasion of the emeritate symposium of Hans Zantema.


Logic Colloquium, August 1999 Utrecht.

Tutorial course, 169 pages, contents:

  1. Knots, Braids and Abstract Reduction Systems
  2. Decreasing Diagrams
  3. Infinite Diagrams
  4. First-order Term Rewriting Systems
  5. Critical Pair Completion
  6. Orthogonal term rewriting systems
  7. Transfinite rewriting
  8. Recursive Path Orders with Stars
  9. Higher-order rewriting
  10. References 





Wolfram-seminar v0