# About Maurice Sion

*A transcript of a speech given by Nassif Ghoussoub*

In the late seventies, Maurice and I were invited to a conference in Crete. We flew together with Emily to Greece, and as we were ready to go through customs in Athens, I told them: Don’t wait for me as I expect they will be asking me lots of questions with my Lebanese passport. The civil war was raging in Lebanon and as expected, refugees were flooding the Mediterranean.

To my surprise, Maurice said: Actually, with my background and my birthplace, I bet you that my custom clearance will take longer than yours. And he was right. I think it was then when he first told me that he was born in Macedonia (then in Yugoslavia) and how --like many European Jews—his family was trying to escape the expanding Nazi occupation of Europe. Maurice knew about discrimination. He knew about displacement. His family eventually fled to Greece, Turkey and then ended up spending his teenage years as a refugee in a small Christian village in the mountains of Lebanon: Mazraet Yachouh. I couldn’t believe my ears: Mazraet Yachouh is only 5 kms away from my own hometown, Beit Chebab.

Maurice had happy memories of his time there. He felt safe there, though briefly under French Vichy rule. And I will always wonder whether that was the reason why, 35 years later, he gave me so much friendship, support, warmth and affection. Emily didn’t mind me much, and so I sort of became the oldest son of the Sions (Sorry Chris). I say that because the Sion’s home was always open to me. I could come and go, visit, hang out and eat, invited or not. Chris and Sarica were nothing short of a brother and a sister to me. Derek was too young and we probably ignored him … or was it the other way around? So early on, Maurice and his tightly knit family became my family. It is because of Maurice that I stayed at UBC, and I have always been grateful for that.

**Maurice was a Mensch, an amazingly serene human being.** I always wondered what was he thinking about --aside from mathematics - whenever he went to his island by himself for weeks on end? Ivar Ekeland and I called his island Ile Maurice.

**Maurice was a man of few words, **but every word counted and none was redundant or misplaced. **Maurice was never judgmental.** He just left you alone.

**Maurice was a generous man.** I remember a department with a vibrant social life, believe it or not, thanks to parties and gatherings at the Sion’s house on Chancellor boulevard. Friends were always welcome to ride his horses at his ranch on Francois Lake and share his island, Ile Maurice.

**Maurice was an inspiration to many young researchers.** They were naturally drawn to him: Ed Perkins and I of course, but also so many other postdocs and visitors such as J. M. Bismut, Sapounakis, Elias and Paula Saab, Jean Pellaumail and many others. We worked, we toured and we partied together, often at the Sion’s house.

**Maurice was a true scholar:** He did, of course, his research in mathematics and I will say a few words about that later, but he was also interested in the genesis and the progress of the human thought intellect. As many of you know he was fascinated by measure theory, but also by its evolution throughout history. His paper “History of the notion of magnitude” starts with the pre-Greek period and ends with Weierstrass, Dedekind, and Cantor.

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*Dear Professor Loewen,*

*I am sorry to hear of Professor Sion's passing. I never knew him (he retired six years before I was born!), but his article "History of measure theory in the twentieth century" (translated into Italian for the Enciclopedia Italiana) was one of the first things I read during my first USRA, on Brownian motion. The article is elegantly and engagingly written, and evokes a subject that turns first-year calculus on its head in a way that very much appealed to me. I still consult it every few months to see how much of the story I am able to follow, and to enjoy the author's obvious enthusiasm.*

*Best, Kyle MacDonald*

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**Maurice was a hugely principled man.** He stood his ground against misguided authority. Now if you think that the math department speaks truth to power now, you should check the lessons in conviction that Maurice gave to the Dean of science then. And those of you who wonder why we have the current departmental constitution: It is because the department wanted Maurice to be head and the Dean didn’t. And guess who prevailed.

**Maurice was a leader.** Besides being a very reluctant head, I must say, he led this department through many major initiatives.

Let me start with Maurice’s pride and joy. The Quadra Institute

**John Fournier: **

*In the late 1960’s and early 1970’s, there was a sentiment in the coffee room that many of us would benefit by learning about important topics that we had missed in graduate school. It seemed that we were too distracted on campus to do that. With Maurice’s leadership, we started having week-long summer meetings in southwest BC, but usually not at UBC. I remember going twice to the University of Victoria and once to Galiano Island for such events. The meetings were called Quadra Institutes. Being away from home and work led to more conversations with colleagues about mathematics.*

*Typically, there was an organizer with some background on the topic. That person would assign subtopics to colleagues and postdocs, most of them not experts. I was the organizer for one on singular integrals, with help from David Boyd and two postdocs. The other speakers that week were not experts. There was no expectation that the content of any talk would be new to experts. In other years, we looked at Morse theory, Frank Adams’s book on compact Lie groups, and classical Greek mathematics. Two that I missed were on Probability and Applied Mathematics.*

Maurice was the Chief organizer of the International Congress of Mathematicians held in Vancouver in 1974. This is a huge endeavor. Several years or hard work starting with making the bid to the IMU 4-5 years prior, winning it and organizing all the logistics. That ICM put UBC Math on the map. To many, it was the most enjoyable and memorable ICM ever. Wreck beach and an abundance of weed also contributed a great deal.

**Maurice was one of the most prominent mathematicians in our department.**

- 1951 PhD, Berkeley. Advisor: Anthony Perry Morse

+ A first counterexample (1954): Is a function constant if all of its second partials vanish everywhere and all first partial vanish somewhere in a connected domain? Yes if C^n+1 (Morse) No if C^n (Sion)

For first partials Yes if C^n (Morse) No if C^n-1(Whitney)

— 1955-57 Institute of Advanced Studies, Princeton. He overlapped with Einstein, Nash, Von Neuman.

+ Extending Von Neuman's Min-Max theorem, using combinatorial KKM, Knaster, Kuratowski, and Mazurkiewicz Combinatorial and not Hahn-Banach or fixed point theorem.

Jean-Michel Lasry: Le mec du min-max? C’est vrai? Il est la?

+ Another counterexample: A game without a value

— 1961 Assistant professor at UBC

+ Variational measure (from Borel in Paris to Tamarkin-Morse-Sion in Berkeley)

+ The current theory of analytic sets (Bressler-Sion) On capacitability and measurability (Lusin’s mistake corrected by Souslin)

— 1968 A textbook: Introduction to the methods of real analysis

S.J. Taylor: This book is an unusually condensed account of the theory of measure and integration, with the relevant topology. In spite of its brevity, the coverage is adequate for a basic two-semester course in real variable theory at the graduate level. There are very few redundant words in the text, and the notation chosen results in unusual conciseness; so that each page of the book contains as much material as one normally expects on two or three pages. In spite of this, care is taken to build up an intuitive feeling for the concepts introduced, and the book succeeds in its avowed aim of bringing out the relation between concepts arising in different areas. This is done by theorems rather than by an abstract formulation of definitions relevant to more than one area.

—1970, Invited speaker, International Congress of Mathematicians, Nice, France A huge honour reserved for the few among us. (Group valued outer measures)

—1973 A Springer lecture notes: A theory of semigroup valued measures

—1981 Vindicated by the school of Laurent Schwartz. The stochastic integral as a vector measure (It all fits). 1992 Last paper: Outer measures and stochastic integrals (Without martingales)

—1989 Retired from UBC: Ed Perkins and I organized a conference in his honour. Gustave Choquet, Gabriel Mokobodski, Heinz Bauer, Claude Dellacherie, etc…Amazing crowd.

—1989-2011 Visiting professor, Universite Pierre et Marie Curie. Active member of the Choquet Seminar

—2012 Member of the inaugural class of Fellows of the American Mathematical Society.

This is a very short summary of Maurice’s rich life. A life that enriched mine and so many other lives.