In Memoriam: Maarten van Emden

Maarten van Emden (Dec. 31, 1937 – Jan. 4, 2023)

Bio by Eva van Emden:

Maarten was born on December 31, 1937, in Velp, the Netherlands. His early childhood was spent in the Dutch East Indies, although he also attended a boarding school in Australia for a short time.

He did his national military service in 1959–1960, serving as pilot and commissioned officer. He attended national flight training school and worked for KLM as a pilot from 1960 to 1963. After that, he returned to university and completed an MSc from the Technische Hogeschool Delft, the Netherlands, in 1966 and a PhD in computer science from the University of Amsterdam in 1971. His dissertation was titled “An Analysis of Complexity.”

Maarten spent 1971 to 1972 as a postdoctoral fellow at IBM T. J. Watson Research Center and then joined Machine Intelligence at the University of Edinburgh as a research fellow. In 1975, he immigrated into Canada to join the faculty at the University of Waterloo. He moved to the University of Victoria in 1987. His visiting fellow positions include University of Edinburgh in 1980, Imperial College (UK) in 1982–1983, and NWO (Netherlands) in 2000–2001.

Maarten had a wide range of interests. Beyond mathematics and computer science, he was interested in the history of science, language and writing, and architecture and design for sustainability. He loved a good conversation about ideas, the more technical the better. Physical activity was an important part of his life: he bicycled to work, ran, swam, and enjoyed many other forms of exercise. Brain health was also important to him, and he practised transcendental meditation for many years.

He continued to take regular walks around the neighbourhood until shortly before his death, and remained mentally healthy until the end. This December, his condition declined with the effects of Parkinson’s disease and heart failure. He died in hospital on January 4, with family members present, less than a week after the death of his wife of more than 50 years, Josefa.

See also:

Bob Kowalski:

Maarten and Jos were dear friends for over fifty years, dating back to Maarten’s arrival in Edinburgh as a research fellow in Donald Michie’s group in 1972. We worked together, first on separate research grants, held by Bernard Meltzer and Donald Michie, and later on the same grant held by my PhD supervisor, Bernard Meltzer. Our intense collaboration in Edinburgh came to an end when I moved to London in 1975 and Maarten and his family moved to Canada.

Maarten, Jos and their daughter, Eva, visited us in Wimbledon during Maarten’s sabbatical in the 1982-83 academic year. Other visits followed for shorter periods, and they were always an occasion for lively discussions and enjoyable informal activities. Maarten was a polymath with a wide range of interests and expertise and with a gift for writing both clearly and entertainingly. It’s a comfort to know that their daughter Eva has inherited her father’s writing talents.

I will miss Maarten greatly, and my family and I will miss both him and Jos.

I have been looking through my pile of old publications, grant applications, final reports, referees’ reports and other correspondence, to remind myself of my research collaboration with Maarten. The most well-known is our paper on the semantics of Horn clause logic programming. The first version of the paper was completed in February 1974, as memo no. 73 of the Department of Computational Logic, School of Artificial Intelligence, University of Edinburgh. It was also “reproduced” as a technical paper, MIP-R-103, by the Department of Machine Intelligence, Edinburgh.

At the time, I was employed by Bernard Meltzer in the Department of Computational Logic, and Maarten was employed by Donald Michie in the Department of Machine Intelligence. You can probably imagine some of the politics that were involved. For a more informative and more entertaining account, you can not do better than to read Maarten’s own essay, reflecting on those times:

As Maarten mentions, he was employed by Donald Michie to work on memo functions. Maarten also mentions that sixteen years later, after working on memo functions in Edinburgh “I read the great book of Abelson and Sussman, where they tell first-year MIT students how memo-izing changes a recursively implemented Fibonacci function from exponential to linear complexity”. You can say the same about tabling in Prolog today.

We submitted our semantics paper to the Journal for the Association for Computing. We had two reviews, neither of which were very enthusiastic. One reviewer failed to respond to the revised version of our paper, and it wasn’t until March 1976, two years later, that our paper was finally accepted, without receiving the delinquent reviewer’s second review. And it was not until October 1976 that our paper was finally published.

The inspiration for our semantics paper was Dana Scott’s unpublished paper, “Outline of a Mathematical Theory of Computation”, which had been circulating in Edinburgh since 1970. Although there was a separate Department of Computer Science in Edinburgh, most of the interest in theory of computation was in Donald Michie’s Department of Machine Intelligence. Rod Burstall was the driving force, and his PhD students included such later luminaries as Gordon Plotkin and Michael Gordon.

Maarten was more of a computer scientist than me, and he suggested that we investigate Dana Scott’s fixed point semantics for functions and see if we could adapt it to the semantics of logic programs. I was marginally more of a logician than Maarten, with an interest in model theory, and a keen aversion to recursion theory. The highlight of the paper for me was the discovery of the minimal model semantics. When we sent the paper to Alain Colmerauer, he commented that the three equivalent semantics defined in the paper captured his own intuitions about the semantics of Prolog. It was one of the nicest things that Alain ever said to me.

Krzysztof Apt:

I learned with great sadness that Maarten van Emden and his wife Jos passed away a couple of days ago.  I have known Maarten for 45 years. I owe him great thanks for introducing me to logic programming and constraint programming.

I first met Maarten in 1977 at a conference in New Brunswick in Canada and we have remained in touch since then.  I was then 27, twelve years junior of him, and my knowledge of computer science, a subject I have never studied, was very limited. During the conference Maarten introduced me to a completely unknown to me topic, logic programming. His enthusiasm was infectious and he kindly mentioned that we might cooperate on some natural open problems he identified.

After my return to the Netherlands our contact continued by mail: recall that it was before the advent of email and the overseas phone calls were out of question due to their high costs.  This and the fact that we also worked on other topics explains why our paper on the subject was finalised only 4 years later and eventually appeared in print in 1982. It became one of my most cited publications.

In 1988 I visited Maarten after the ICLP conference that took place in Seattle: Maarten has moved some time earlier from Waterloo to Victoria at Vancouver Island. He showed me then his recent paper written jointly with his PhD student Keitaro Yukawa, titled Logic programming with equations (the paper appeared in 1987 in the Journal of Logic programming). This elegant article introduced me to the fast growing research area concerned with the amalgamation of logic and functional programming. It helped me and my colleagues at CWI to formulate our part of an European (Esprit) project that involved 16 teams from several countries.

Maarten’s 2001 paper, written jointly with Timothy Hickey and Qun Ju, titled Interval arithmetic: From principles to implementation introduced me in turn to the field of constraint programming and had an important impact on my research in this area. I found Maarten’s comments on this important paper most helpful and illuminating.

My last scientific interaction with Maarten was two years ago when jointly with Tony Hoare I was putting together short testimonials about Edsger Dijkstra, written by researchers who have known him. You can find Maarten’s fine contribution at the end of Edsger W. Dijkstra: a Commemoration.

Throughout the years we maintained regular contact. I visited Maarten in the summer of 1999, while he spent shortly after his sabbatical at my institute, CWI, in Amsterdam.

By focusing only on research I am doing injustice to Maarten.  I have always been impressed by his broad interests, his curiosity, and his original scientific ideas.  He was an extremely nice, kind, gentle, and selfless person.  On a number of occasions I enjoyed his and Jos’ hospitality and was moved by noting what a great couple they formed.

Early last year Maarten wrote to me about Jos’ and his illnesses. I did not expect that their lives would end so soon.  I shall miss them dearly. They were great friends and marvellous and inspiring people.

Jimmy Lee:

I was the second last student out of Maarten’s ten PhD graduates according to the Mathematics Genealogy Project.  Our first encounter dated all the way back to 1985 when I took the Data Structures course from Maarten in my third year at the University of Waterloo.  That was not a very exciting experience.  The only thing I could recall was that Maarten always asked us to prepare the coursework at home and reserved the last hour of each week for us to ask him questions about the course.  Obviously, nobody asked any questions and Maarten would happily declare the end of class after two minutes into the class.  Maarten was a pioneer in what today is called “Flipped Classroom”.  In my fourth year in 1986, I took the Logic and Functional Programming course from Maarten and that was life-changing.  I fell in love with Prolog and logic programming.  I was also applying for postgraduate studies at that time.  When Maarten agreed to take me as a Master’s student in early 1987, I just accepted the offer and never looked back. 

I started working for Maarten on the IBM-sponsored TuplePipes project even when I was in the final semester of my undergrad studies.  By the time I started my MMath degree officially in the fall of 1987, Maarten had already moved to the University of Victoria (UVic).  I was supervised by Maarten remotely and looked after locally by Mantis Cheng, who was a PhD graduate of Maarten and later became a long time colleague of Maarten at UVic.  In December, 1987, Maarten invited me and Mantis to visit him in Victoria.  While being there, I submitted my application for PhD studies.  In the fall of 1988, I joined UVic as a student and Mantis joined as a faculty member.  Two of my fellow classmates, David Rosenblueth and Paul Strooper, also joined as PhD students a year prior to us.  In 1986, Eric Manning from Waterloo joined UVic as the Dean of Engineering.  He said his goal was to turn UVic Engineering into “Waterloo of the West”.  I can tell that taking Maarten and his entire research group over could be part of Eric’s grand plan to achieve his goal.

I would like to share four pieces of anecdotes between Maarten and I during my four years at UVic.  First, Maarten was fond of Chinese Dim Sum.  In (Waterloo and) Victoria, I was frequently invited to join his Saturday Dim Sum brunches with Mantis.  The conversations during the meals were 95% technical discussions.  To me as a young grad student, the meals were sumptuous both in food and learning.  Second, Maarten was a gentleman, but strict with academic and writing standards.  Seeing Maarten in the weekly meetings was always a nerve wracking experience when I was a student.  Having to submit my writing to him was even worse.  He often could not read past the first page, and returned my writing to me.  Overly confident with my English writing skills, I “confronted” Maarten one day.  That did not end in a shouting game.  He only said to me in his typical calmest tone, “Jimmy, there’s no need to argue.  Let’s use Strunk & White as the standard.”  I can never thank him enough for his insistence on rigor in technical writing even until today.  I am not sure if I can ever attain the standard he wanted.

Third, I failed my PhD candidacy examination and had to redo it.  I was totally devastated.  When I told Maarten that I wanted to give up, he said, “Jimmy, don’t quit.  I am willing to coach you until the end.”  Those were the most touching words that were said to me in my life.  As much as Maarten was a strict supervisor, he had his side of loving care for his students.  Fourth, we were invited to Maarten’s place for a gathering a few times.  That was where I met Jos and Eva.  I could still remember the homemade bread made by Maarten.  The food was simple but the company of Maarten’s family and fellow classmates was always part of my fond memories.  Learning from Maarten, I now organize a gathering for all my former and current students every year around Xmas.

Upon graduation, I returned to Hong Kong for a faculty position in 1992.  That was the time before we had Zoom or the likes.  I met Maarten in person again the first time only at ILPS-94, which was held in Ithaca.  Maarten was an Invited Speaker there.  I was chatting to him while enjoying the food and drinks at the conference reception.  Our conversation quickly converged to my PhD work.  Maarten suggested that I documented what I thought as mundane details of interval operations.  I impatiently asked Maarten whether that was publishable.  He said, “Jimmy, the purpose of writing/publication was to avoid duplication of effort.”  I am glad that the reception was held in a room with low light.  Or else, people must have been able to see my face burning red.  I felt extremely embarrassed since I was “contaminated” so easily.  I felt extremely embarrassed since I had already forgotten the true meaning of being a researcher only after two short years in the materialistic world.  It was Maarten who brought sanity into my mind again.

Held in Boston, CP-96 was my first conference in constraint programming.  At the end of the conference, the PC Chair, Eugene Freuder, had a few conference coffee mugs left, and decided to use some excuses to give them away.  I received a mug for the Best Presentation Award.  Maarten congratulated me and told me a few people saw my presentations and asked him who that strange face was.  He said he replied proudly, “He was my student.”  My former supervisor’s words of recognition were just music in my ears.

During the last thirty years, I kept in touch with Maarten.  Besides seeing him in conferences a few times, I also made a handful of visits to Victoria.  We also wrote regularly to each other a few times a year.  The last time I visited Maarten was in 2014 when he enthusiastically discussed his paper with me upon my arrival.  We also had a 5-hour smoked salmon and bagel brunch at his place with Jos and friends.  That was the first time I saw Maarten singing.  Jos and Maarten visited Europe and Cambridge that summer.  My elder son, Jasper, was lucky enough to have attended Maarten’s talk at Microsoft Research at Cambridge, and was invited to lunch together with Maarten, Simon Peyton-Jones and Tony Hoare.  Jasper was blessed to have such an opportunity.  I was going to visit Victoria in June, 2020, to see Maarten and Jos.  There was the dreadful pandemic for all and the rest was history.

Just a few months ago, I started planning for a visit to Victoria in 2023 but everything was too late.  The lesson was that if one wants to see someone and say how much you respect and love them, don’t wait.

I hope my short commemoration piece shows the different facets of Maarten, as a scholar, a supervisor, a mentor, a teacher, a gentleman and a friend.  To me, Maarten was my academic father.  My life would not have been the same without him accompanying me at different stages.  His teaching and kindness will always stay with me.  I will miss Maarten and Jos dearly.

Andre Vellino:

My grief at the news of Maarten’s passing is disproportionate with the extent to which I knew him. It feels like I have lost a mentor and a good friend, even though we didn’t spend all that much time together and only wrote one (wonderful, but completely ignored and uncited) paper together – no doubt due to its relatively obscure publication venue in a Chess journal.  I’m sure its title didn’t help either (“Understanding the Human Window”) since the paper was largely about the Chinese Room argument.

My first contact with Maarten was around 1990 or so when I was at BNR’s Computing Research Lab, led by Peter Cashin.  Bill Older had developed BNR Prolog – a constraint logic programming system for computing interval arithmetic relationally – and we were wanting some expert eyes to tell us whether this was as cool and innovative as we thought it was.  Maarten had recently left the University of Waterloo for the University of Victoria.

I can’t remember what he told us about BNR Prolog but what we said to him about it must have left an impression – a significant number of his collaborative articles from 1995 onwards were about constraint interval arithmetic, notably Interval arithmetic: From principles to implementation with Tim Hickey.

I just noticed an interesting coincidence looking at Maarten’s Google Scholar profile.  One of the notable computer scientists at the Computing Research Lab was Bill Williams best known for having developed HeapSort in 1965.  I see that Maarten wrote a paper in 1970 on improving the efficiency of QuickSort.  Perhaps it was a hobby in that generation of smart computer scientists to think deeply about sorting algorithms.

One thing I remember well was the aura of authority he exuded about logic programming.  When he expressed an opinion about something – anything really, but logic programming especially – it just sounded true beyond the shadow of a doubt.  I sometimes thought that just having a dutch accent made what he said sound more true than it would have spoken with an English or American accent :-).

We stayed in touch in a light kind of way.  In some of those exchanges I learned that he had something of an interest in meditation – so we talked about the wisdom traditions that emphasised meditation.  I think he tried it and appreciated it.  He was always open to new ideas and perspectives.

In 2008 I was in Victoria visiting friends of my family and he suggested we go for a walk together in the arboretum (more photos here). It was then that I first observed his sensitivity to nature – which rather surprised me for such an intellectual man.

I was quite struck with how we collaborated on our paper on the Chinese Room argument.  We had quite different views about Searle, but we found common ground in this paper.  He was always willing to concede a point if it was well argued. I loved how he wanted to honour and expand upon a long-lost idea of his own mentor Donald Michie (the idea of “The Human Window”).  He was quite into the history of AI and in writing his essays on his blog at that point.  I feel sure that editing and publishing these essays on The Programmer’s Place blog would be a great way of honouring his memory.  At the very least, I think he deserves an entry in the Wikipedia, so I started an entry for Maarten in the Wikipedia.

Thank you Maarten for sharing so generously of your time and insights.  You helped me in more ways than you know and I continue to be grateful.

Randy Goebel:

As others have already commented, Maarten always enjoyed a good technical conversation, and on the occasions when people like Bob and Krzysztof would visit and I was lucky enough to participate, I too loved the technical conversations.

Losing old friends tells me that I should spend more time celebrating life, and be thankful for the good friends I have had.

As Mantis, Jimmy and André also know, Maarten was a mentor for me, and graciously shared his considerable knowledge of logic and Prolog, making me a better scientist.   I have such fond memories of working with him at his house in Waterloo, with Jos busy around us, and Eva playing around us.   And then in Victoria, visiting him at his home and always enjoying his company and advice.

Maarten also invited me to his home in Wimbledon, when he was on sabbatical at Imperial College, and I have fond memories of travelling back and forth from Jos and Maarten’s home to Imperial.  Maarten also introduced me to Bob Kowalski, of course, but also Keith Clark, Marek Sergot, and Frank McCabe.

An item noted by my family:  Maarten visited our family when we lived in Tokyo, and I was a professor at the University of Tokyo.  I was reminded that Maarten spent time with my children and wrote a little paper memory game that he did with them, which had Kanji characters written on one side of a piece of paper, and they had to remember which paper tag was the match for any Kanji character.  Perhaps the greatest accomplishment of all was that my youngest daughter Kelly, then 6, convinced Maarten to eat at a McDonald’s in Tokyo … first time ever for him at a McDonald’s (maybe last too, I don’t know ;-).

We will always miss the people we have come to love and respect … and I have learned to cherish their memory and my good luck at knowing them.

Keith Clark:

I first met Maarten in 1973 in Edinburgh.  I was visiting Bob Kowalski and giving a talk based on a research report I had recently written.   I cannot remember Maarten’s comments but I am sure they would have been perceptive. It was on this visit that Bob introduced me to the elegant concept of logic programming, and I was immediately sold on the idea.  Maarten had been previously exposed to the concept, and I know he shared my enthusiasm.

In 1979, after Maarten had moved to Waterloo, he and I produced a research report entitled “Consequence Verification of Flowcharts” that was later published in IEEE Transactions on Software Engineering.  The approach was to transform a flow graph version of the flowchart into a set of Horn clauses that ‘computationally’ described the input/output relation computed by the program.  Verification of these computational rules was then reduced to showing that they were just theorems of a first order theory that declaratively and correctly described the input/output relation. I recall that Maarten did nearly all the writing of the report in his clear and erudite style. One of my regrets is that this was our only joint paper.

The next year, while I was on sabbatical at the University of Syracuse where Alan Robinson was based, I visited Maarten in Waterloo.  I had driven from Syracuse to Maarten’s house.  We were talking in his front room soon after I arrived when Maarten noticed that someone seemed to have parked their car on the front lawn of the house opposite.  It was my rental car!  Being unused to automatic cars I had failed to put the car into park and I had failed to apply the handbrake. The car had rolled back down Maarten’s driveway across the road and had come to rest on the front lawn. I rushed to retrieve it.  As always Maarten remained calm, but also quite amused.

After Maarten moved to Vancouver I visited him several times. My visits were always enjoyable and stimulating.  On my last visit about six years ago Maarten and I started each day with a brisk walk from his house to the university.  I think it used to take us the best part of an hour.  It was a good way to start the day. It was typical of Maarten whose motto could have been “Mens sana in corpore sano”.

I still cannot believe I shall not see Maarten and Jos again. Both were so calm and measured in their views, and hospitable.

Mantis Cheng:

Maarten and I had worked together for almost 40 years, first at the University of Waterloo and then at the University of Victoria until our retirements. We enjoyed our companies eating at many Chinese restaurants in Waterloo, in Victoria and in many cities around the world. We travelled numerous times together in Canada and in the US, visiting campuses, and attending conferences around the world, first as supervisor/student, then as colleagues, and then as family friends living in Victoria for over 34 years.

While at Waterloo in the mid-80s, we worked on the development of various versions of Waterloo Prolog, which was eventually commercialized into IBM Waterloo Prolog by the Waterloo Computer Systems Group. In the late 80’s, we visited Bell Northern Research (BNR, later became Nortel) about their work on BNR-Prolog and interval constraints with real numbers. This was when I started to become more interested in distributed real time systems and our research interests since then started to diverge. Maarten had always been interested in programming in general, and logic and functional programming in particular. I worked as a teaching assistant for him in many courses related to logic and functional programming, which eventually became a topic in my doctoral dissertation. Maarten was good at understanding theoretical concepts, while I was good at implementing those concepts in practice; so we complemented each other’s research interests.

Since we moved to the University of Victoria in 1988, we continued working together as colleagues. He was hired primarily as a research chair to develop logic programming further; while I was hired to assist him in his endeavour. For the first 10 years, we still worked on many projects related to logic and functional programming, and invited many of his colleagues visiting us, including Bill Older from BNR, Stott Parker from UCLA, Donald Michie from the Turing Institute, Krzysztof Apt from CWI Amsterdam, Keith Clark from the Imperial College, Jonathan Schaffer and Randy Goebel from the University of Alberta, etc. Maarten gradually got more involved in teaching first year programming; this was when he wrote his first book on “Elements of Programming”. He very much enjoyed the challenges of teaching beginning programmers. His approach was similar to Dijkstra using first principles in reasoning precisely mathematically about problem solving. He maintained a blog, A Programmer’s Place (, which discussed many topics related to his personal interests and history about programming. His approach to programming was more about learning how to walk than how to run, more about how to think clearly than to learn to be proficient in using a particular development tool. Maarten and I spent numerous lunches together discussing various topics related to teaching and software design. This was a fun time working together at the University of Victoria.

We spent the better part of our lives, over 34 years, working and living in Victoria. He was diagnosed with Parkinson in the last few years of his life, but otherwise he was healthy. We enjoyed listening to classical and Jazz music, eating Chinese foods Dim Sum in particular, cooking Indonesian cuisines at home, and sharing his knowledge and skills about gardening. Maarten and Jos loved gardening. They loved to have company. We spent many parties at their contemporary open-concept minimalist home. Jos always made me my favourite coffee and roasted hazelnuts. Unfortunately Jos’ dementia condition was deteriorating faster than Maarten’s Parkinson disease; so Maarten had to leave her in a care home for dementia patients, while he spent his end of life in another care home. I am saddened with the passing of Jos and then Maarten within a week, but I am happy to know their sufferings are over now. Rest in peace for both of you. It has been fun to meet and know you both.

Veronica Dahl:

I first became acquainted with Maarten’s marvellous mind in 1976. I’d borrowed his technical report with Bob Kowalski “The semantics of predicate logic as a programming language” from Alain Colmerauer’s bookshelf, and immediately upon reading it, decided to emulate their writing, which I found super clear. It was like a flashlight making concepts shine – concepts I’d been well exposed to and was applying daily, yet never quite captured in such a precise, elegant, pedagogical manner. I studied it once more, focusing this time on writing style. I’ve since had many conversations about writing with Bob, but somehow none with Maarten. Re-reading our email exchanges of the past few years, I am glad to see that I did get around to thanking him… in 2016! He’d kindly praised an article of mine and thanked me for having by the way learned a few Spanish phrases from it, and I replied it was only poetic justice, thanking him in turn for how his and Bob’s writing had inspired mine early on.

In 1977 I had the pleasure of meeting Maarten in person at the Logic and Databases Workshop in Toulouse. Since, I have much relied on his insight: he very kindly – up until last year, when I consulted him about the “50 years of Prolog” article!! – gave me useful feedback whenever I asked, not only on scientific questions, but also about university politics, which he knew much more about than I, an outsider in so many respects. Long ago, I don’t even remember where, we coincided side by side on a bus towards a conference’s social event and the conversation derived to the subject of meditation, which I learned he practised assiduously. I asked him to explain how he did it. It was another source of inspiration: I started meditating myself, and never stopped. A few years later he recommended to me “My stroke of insight”, by brain scientist Jill Taylor, opening up a series of conversations that related both to our field and to its invisible links to subjects usually considered more esoteric.

Maarten was also very supportive and encouraging of my erratic incursions in music. Once when his visit to Eva, who then lived in Vancouver, coincided with a gig of mine, he honoured me with his presence, and then put me in contact with a latin venue in Victoria where I subsequently got a gig too. Another time we chanced to be on the same plane when I was returning from Spain and he was coming back from a visit to his father in Amsterdam. During the trip, he convinced me to write a parody for Maurice Bruynooghe’s upcoming retirement party, which (for better or for worse :-)) I did.

After Jos and Maarten moved to Victoria, a ferry boat ride away from Vancouver, I would go visit them whenever I was there, which unfortunately hasn’t been very often, but I fondly remember talking shop and metaphysics in their sunny garden while eating their delicious strawberries straight from the ground, or discussing music and many other subjects after dinner. Conversely, lunch at my home was a must whenever possible during their visits to Vancouver.

Last summer I tried to arrange to visit Maarten while on a brief trip of mine to Victoria, but unfortunately we did not manage to connect in person. However, we did have a nice chat on the phone. I am deeply saddened that it was the last one.

The LP field has lost one of its greatest minds; the world, a most valuable human being, and I a dear colleague, friend and mentor of unusual scope and depth of interests. I will miss him and Jos greatly.

Photo from a panel session we both participated in

Photo from ILPS’93, Vancouver

The photo below is from the Logic Programming Workshop on the Queen Mary, Long Beach, August 1981. Maarten is in the first row, the third from the left. John McCarthy is in the second row, the second from the left. Alain Colmerauer is in the second row, in the centre, wearing a black shirt. Alan Robinson is in the back row, directly under “Winston” on the sign “Sir Winston Churchill’s”. There are many other famous people in the photo. Can you recognise them?