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[{Image src='sintzoff_michel.jpg' caption='' height='150' alt='Michel Sintzoff' class='image_left'}]
!!The Humble Humorous Researcher
!!A Tribute to Michel Sintzoff
Axel van Lamsweerde[1]
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Many of us lost a close colleague on November 28, 2010. More than that: we lost a friend. One
that we used to meet regularly, all over the world, always listening to us, making interesting
comments and suggestions on our work, joking on every occasion and making us discover how
much fun our business is.
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Rather than reviewing his work in detail, this note puts more focus on Michel’s rich
personality, with the hope that it will bring back fond memories among those who were lucky
enough to share some good times with him. The style is intended to be personal and informal.
Michel would have hated anything different, to be sure.
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Born in 1938 in Brussels, Michel completed his master’s degree in Mathematics at the
Université catholique de Louvain (UCL) in 1962. After two years of civil service as a maths
teacher in Katanga (Congo), he entered the MBLE Research Laboratory in Brussels in 1964
(MBLE stands for “__M__anufacture __B__elge de __L__ampes et matériel __E__lectrique”). This was a branch
of Philips Research Labs specifically dedicated to background research in applied mathematics
and computing science. After 18 years of research in programming languages, formal
semantics, program analysis and concurrency at MBLE, he joined the newly founded
department of Computing Science at UCL in 1982 with new interests in diverse areas such as
proof systems, control theory and dynamical systems. Michel contributed to the PhD work of
dozens of people in Belgium and France, as supervisor or contributor, without ever having been
interested in getting a PhD himself. He received a Doctorate Honoris Causa from the Université
Joseph Fourier in Grenoble (France) and was a member of the Informatics section of the
Academy of Europe. Michel was an Emeritus Professor at UCL since 2003. The two of us were
face to face in the same office at MBLE Research for 10 years (1970-1980), and had adjacent
rooms at UCL for another decade (1993-2003).
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Many consider Michel’s paper ''Calculating Properties of Programs by Valuations on Specific
Models'' (Proc. ACM Conference on Proving Assertions about Programs, 1972) as the precursor
paper on abstract interpretation. This paper and others he wrote around that time on program
verification and type discovery are heavily cited in the paper generally considered to have opened the field (Cousot and Cousot, 1977). The technique described in his 1972 paper was
simultaneously implemented in Paul Branquart’s optimizing compiler for Algol68, confirming
how powerful it was.
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At that time Michel had a strong interest in the precise definition of language semantics; he was
co-editor of the Revised Report on Algol68. To distract him from this Herculean task, I used to
challenge him with my own research problems. This resulted in seven joyful years of joint work
on invariant generation and formal derivation of concurrent programs. I noticed that Michel
kept citing this work up to his very last papers (e.g., ''Mathematics of Program Construction
2008''). Recent interactions suggested that he was still interested in some joint work around this,
and I regret now not having picked up the gauntlet.
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With a rich harvest of European grants and PhD students, Michel expanded his research
horizons as he moved to the academic world. While staying fairly active in type theory and
program verification, he developed techniques for formalizing and composing design decisions
in a modular way; for specifying, refining and composing proof structures; and for synthesizing
control information for multiple types of systems, notably relational programs, reactive systems
and dynamical systems. His earlier 20 years outside the academic world inoculated him against
the ''publish-or-perish'' syndrome. Michel published relatively few papers, but these were
consistently innovative and thought-provoking. Quoting Cliff Jones, ''I personally rate him one
of the most imaginative researchers I've known. He had exotic ideas and worked them out
carefully, a rare combination''.
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Michel was also instrumental in collective projects such as ''Raisonner pour programmer''
(Dunod, 1986), a book on program design strategies and tactics which at that time had no
counterpart of such quality, in my opinion. The book’s author, Anna Gram, was a joke name for
a largely French working group whose other members were J.C. Boussard, J.P. Finance, C.
Gresse, P. Jacquet, G. Perrin, A. Quéré, P.C. Scholl, L. Trilling and J. Voiron.
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From the very beginning of his research career Michel had two obsessions: ''technical precision''
(so much needed in software engineering research) and ''formal construction of correct artefacts''
(as opposed to verification of possibly poorly designed ones). Fortunately enough, quite a few
of us were infected by these.
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Michel’s main research tools were paper and pencil. He was often joking about our business by
quoting Edison’s phrase ''1% inspiration, 99% perspiration''. This was measurable by the number
of paper sheets full of formal developments that was accumulating in his trash weekly. His
family found hundreds of handwritten pages meticulously numbered YYYY-MM-nn (yearmonth-
pageNumber). The last page is numbered 2010-11-1a, thus written the day before he
went to the hospital.
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Michel also used to spend a significant portion of his time reading papers and books in many
different areas, including areas not connected to computing science. He kept saying: ''it’s good
to learn from others to refrain from reinventing the wheel''. His scholarship proved invaluable to
those working with him. How many times did we not get relevant references from him that we
would never have read otherwise? How often did we not get directions and technical
suggestions based on his erudition?
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Michel was deeply involved in multiple services to the community. He launched the ''Science of
Computer Programming'' journal in 1981 and was its editor-in-chief until 1999. I remember
lively discussions about the scope of the journal, the initial editorial board and his questioning
of the journal’s name set up by North Holland; he thought that ''Science'' was a somewhat
arrogant claim and ''Computer'' was inadequate (as convincingly argued by Edsger Dijkstra, who
wrote a word of welcome in the first issue). Krzysztof Apt reported that Michel sent
occasionally insightful notes in which he was giving the editors useful suggestions about the
desired directions ''science of programming'' as a field should aim at. I’d like to cite Michel’s
own words in his editorial for that first issue, as I believe them still to be relevant 30 years later:
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%%quote 
SCP is intended to further the publication of systematic and formulated knowledge on
program design. This allows for specific case studies as well as more general techniques
on program development, and implies the use of the classical scientific method, to foster
economy in brainwork and repeatability of the effects of proposed laws. This intended role
should be clearly useful, being at the heart of what can be called the first intellectual
industry in our history: it should assist far-reaching disciplines like programming
methodology, software engineering, and design technology, which themselves underlie
notational systems, support systems, and production systems. […] A forum based on the
written word could facilitate communication within and between generations, and across
unkind boundaries, as exemplified by the library of Alexandria.
/%
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Michel put a lot of energy in the SCP project. The impact of his dedication over 18 years is now
measurable in terms of the impressive number of influential papers that appeared in the journal
during his editorship.
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Michel quite often served in review panels for European, national, and university research
programmes – not to speak of countless thesis committees. As many of us experienced, he
cultivated the art of kindly but firmly raising issues that were right to the point. There is a
French saying ''act as a donkey in order to get the bran'' – something like ''play the fool to catch
the wise''. Michel was exactly like this. He used to naively ask the right questions and could
quickly put his finger on shaky aspects or limitations without ever being destructive or unfair.
When you told him enthusiastically what you thought to be a great idea, he invariably replied:
''on se calme, on se calme'' (''calm down, calm down''), giving you good reasons why your idea had
to be further worked out. Gérard Huet reported a typical anecdote about this. He was presenting
a demo of his Coq proof assistant during a review of a European project for which Michel was
a reviewer. While Gérard was showing complex, elegant proofs Michel asked: ''can you please
prove (a + b)%%sup 2/% = a%%sup 2/% + 2ab + b%%sup 2/% for me?''. He could find exactly the right counterexample. This problem was not at the time solvable in Coq other than giving by hand all the equational steps
involved in proving this identity. It is only a few years later that this sort of algebraic identity
could be solved trivially by the reflection tactic applied to the theory of rings – as a result of
Michel’s constructive criticism.
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Michel has been a pillar of diverse working groups over many years, including IFIP Working
Group 2.1 (Algorithmic Languages and Calculi) since 1968 and Working Group 2.3
(Programming Methodology) since 1976. With typical hospitality he hosted quite a few
meetings in delightful places in Southern Belgium. He reluctantly agreed to be chairman of
WG2.3 from 2003-2006. His characteristic interest in everything made him perfect in the role.
As Jeremy Gibbons said on behalf of WG2.1 members:
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%%quote 
Michel was the longest-serving and most faithful active member of WG2.1, and we have
all felt his influence over the last 42 years. He had a rare combination of excellent insight
in technical matters, a determination always to understand, and a knack for asking
penetrating questions. Even when pointing out flaws or omissions in our work, he always
did so in a very constructive way. It is thanks to Michel that the ALGOL 68 Revised Report
was so much more readable than the original Report: the structured presentation of the
Semantics, replacing the goto style of the original, is due to him, as is the use of
predicates in the syntax, and their use to bring the semantic context conditions into the
syntax.
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We all have fond memories of Michel from the many WG2.1 meetings we have shared.
He was unfailingly kind and welcoming, especially to younger academics, and was without
arrogance or pomposity. We always knew that we had arrived at the right place when we
heard his joyous laughter emanating from the general vicinity of the bar – often in
response to his own jokes, but they were worth it. Dave Wile recalls the meeting in
Ameland, Holland, the week of 9/11, when he was giving the banquet speech: ''He always
loved to tease and instigate trouble. We sat together at the banquet and as I began my
speech, he saw that my notes were on my Palm Pilot. During the speech, he quietly
changed the page so I had no idea where I was or what I was talking about. I certainly
hope he retained that impishness right to the end.'' Michel was loved and respected by us
all, and he will be sorely missed.
/%
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The impressive number of similar reactions within a few hours after circulation of the sad news
revealed how many personal relationships Michel succeeded in creating within the community.
Remarkably, the most common thought emerging from many of these was about how Michel
influenced careers in some way or another. In my case, for example, he decisively stepped in
twice: at the very beginning, to offer me a desk in his MBLE office so that we had a better
chance to work together, and 20 years later, to urge me to apply for a UCL position close to
him. He had a systematic policy of stimulating young researchers. I remember a flight from
Pittsburgh where he proudly admitted this to be his main professional achievement.
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This brings us to Michel’s great humility – explaining the title of this note, with a wink to
Edsger Dijkstra’s Turing Award paper ''The Humble Programmer'' that Michel loved. I never
heard him speak highly of himself. His last wish I am aware of was to avoid any speech at his
funeral, fearing that ''people would say all sorts of things that are not true''. In fact he told me
exactly the same when he retired, discouraging us from organizing a Festschrift on that
occasion. We never heard of Michel being a member of the Academy of Europe, as another
example. After he received his Doctorate Honoris Causa from Grenoble, he kept joking that this
was not a Doctorate Laboris Causa.
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Humility came with an instinctive aversion against any authority argument. I remember when I
had to present our first joint paper at a conference attended by all the big names (the ACMIEEE
International Conference on Reliable Software, 1975). I was terrified by this. To make me
feel confident, he explained how he managed this problem at an earlier conference when he was
in that same situation. As he noticed ''the'' big name surrounded by an admiring court, he jumped
into the circle and told the big name: ''I know you are the Tsar of computing science but you
don’t scare me'' (and he started laughing). This together with some technical verse he had
prepared worked remarkably well. That story helped me a lot on multiple occasions.
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Michel’s distinctive laughter became a legend. It has never been that clear to me what part of it
was controlled and what part was not. Most often it referred to hilarious situations he had
caused and in which he was deeply involved. Typically, after creating the initial state, he
iterated on expiration-inspiration cycles under uncertain termination conditions; every
inspiration triggered a siren, increasingly resonant from one iteration to the other. After a few
iterations, the noisy conversations among hundreds of persons at a conference banquet stopped
and everyone was laughing by contagion. Many of us have plenty of anecdotes to report. My
first exposure to this laughter was on my very first day of work. I was introduced to everyone at
MBLE, room after room. When I entered Michel’s office, he asked me what I planned to work
on. I tried to be as smart as possible and declaimed my lesson. After having listened to me very
seriously, he said: ''very interesting, but are you sure that Philips will pay you for that?'' – then
that laughter when he saw my face. A much bigger, longer one occurred a few years later as
Michel’s wife and children came to the office on a Friday night to catch him. The trigger was
his young boy saying: ''Oh Dad, that’s not like at my school, it’s too easy for you to cheat and
copy each other’s ideas!'' Friday afternoons were particularly enjoyable, from stories to stories
we used to tell each other, intertwined with laughter, to the point that often half the lab ended
up in our room to share our hilarity. Over the years I have interpreted Michel’s laughter as a
recommendation for never taking ourselves or our business too seriously.
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Michel had other extra-professional skills. I remember him once showing me how he could
concurrently write English with his right hand and Russian, his parents’ language, with his left
hand. Speaking of his hands, many will remember the admirable dexterity with which he was
able to serve French fries with two spoons in a single hand – a skill he acquired during student
jobs in Belgian restaurants. His family reported that he practiced regularly this art on Sunday
lunches, the process being sometimes abruptly suspended by the need to write down a fresh
idea he just got.
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I used to meet Michel regularly since he retired. He kept working on things he was interested
in; his last paper, co-authored with Roland Glück and Bernhard Möller, appeared in
''AMAST2010''. He kept saying: ''it’s so great to be emeritus, you feel like being on perpetual
sabbatical''. As Krzysztof Apt wrote to him: ''I understand that you are doing fine, even though
you retired'', he replied: ''replace “even though” by “because”''. When he left to the hospital,
Michel was still working on a new paper (with many references to work from the seventies);
the printed draft, full of red markings, is dated October 30.
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Michel used to say: ''we only have one single life'' to deter people from considering too many
research directions and encourage them to choose the right ones. On a recent discussion about
the need, in my area, to consider bounded ''Achieve'' properties rather than liveness ones, Michel
reminded me that he was for his part only interested in so-called ''S-properties'', that is, properties
that are achievable within Sintzoff’s lifetime. We would never have expected S-properties to
have such a short time frame.
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As Brian Randell said when he was told of Michel’s death, ... ''but he was always so full of life''.
Beyond Michel’s contributions to our field, I’m sure that his kindness, subtlety and deep sense
of humour will remain in the heart of many of us for a long, long time.
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Axel van Lamsweerde
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ICTEAM Institute, Dept. Computing Science\\
Université catholique de Louvain\\
B-1348 Louvain-la-Neuve (Belgium)\\
avl at info.ucl.ac.be\\
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[1|#1] Warmest thanks to Gérard Huet, Jeremy Gibbons, Cliff Jones, Yves Ledru, Krzysztof Apt and Jeanne,
André, Marie, Ivan, Catherine and Paul Sintzoff for their support and input material to this note. Thanks
also to Joanne Allison, Dominique Gallez, Carlo Ghezzi, Lambert Meertens, Bernhard Mōller, Pierre-
Claude Scholl and Bas van Vlijmen for their comments.
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To appear in ''Science of Computer Programming'' (Elsevier) and ''Formal Aspects of Computing'' (Springer-
Verlag).
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[Download the tribute|MichelTribute-veryFinal.pdf]