Her primary research field is probabilistic combinatorics, which involves the study of combinatorial problems applying methods from probability theory. Combinatorics is a subfield of mathematics, concerned with discrete structures. “We are interested for example in the maximum possible number of sets, or other objects, under certain conditions,” she explains. “These types of questions arise in a wide variety of contexts. In addition to probabilistic techniques, I also utilize algebraic methods in my work.” There are numerous applications for combinatorics within mathematics, but also in related areas, such as coding theory and computer science. At the University of Bonn, Professor Sauermann works at the Institute for Applied Mathematics due to the pronouncedly ‘applied’ nature of her research discipline.

She accepted an offer to become a prestigious Hausdorff Chair at the Hausdorff Center for Mathematics (HCM) - a Cluster of Excellence at the University of Bonn. The HCM funds these lifetime chair professorships to enable attracting international scientists of the highest repute. Professor Lisa Sauermann now joins the other current chair holders: Ana Caraiani, Stefan Müller, Sven Rady, Angkana Rüland and Christoph Thiele. Former holders of the Hausdorff Chair include Benjamin Schlein, Massimiliano Gubinelli and Peter Scholze, who is now Director of the Max Planck Institute for Mathematics in Bonn.

**Great success at the Mathematics Olympiad**

Sauermann has been known for her tremendous mathematical talent since her early youth. While attending a special school for mathematics in Dresden she competed several times in the International Mathematical Olympiad, winning four gold medals and one silver - thereby becoming the competition’s most successful participant ever at that time. Upon finishing school Sauermann did her Bachelor’s degree in mathematics at the University of Bonn, where she also taught at the Bonn Math Club for high school students. “When I was a high school student, mathematics was mainly something I did for fun,” she relates. “I have always enjoyed sharing my love of mathematics with younger people.”

**Career in the US**

After finishing her Bachelor’s degree in Bonn in 2014, Lisa Sauermann went to Stanford University, where she completed a five-year program to earn both a Master’s and Doctorate in Mathematics. Her doctoral dissertation earned the Richard Rado Prize awarded by the Discrete Mathematics Section of the German Mathematical Society. Sauermann then worked at Stanford University and at the Institute for Advanced Study in Princeton until 2021, when she became an Assistant Professor at the Massachusetts Institute of Technology (MIT). That same year she was awarded the European Prize in Combinatorics, and in 2022 she received a Sloan Research Fellowship. This fall the 30-year-old mathematician will be accepted into the Heisenberg Program of the German Research Foundation (DFG), which provides five-year grants for outstanding scientists.

**Returning to Bonn**

Sauermann is very glad to be returning to Bonn after nine years living and working in the United States. “The University of Bonn is a superb work environment, and attracts exceptional students,” she says. Her family is very happy too to now be living in Bonn, as she relates: “My two little girls are thrilled about all the ice cream shops all over town.”

## “The University of Bonn is really an exceptional place for mathematics!”

**The shelves in her office are still empty, as the container carrying her books hasn’t yet arrived by ship. Professor Sauermann likes her spacious, bright office at the Hausdorff Center for Mathematics (HCM) at the University of Bonn. She became holder of a prestigious Hausdorff Chair in August at age 30 - a professorial chair created to attract the most brilliant international mathematicians to the University of Bonn. Johannes Seiler interviewed Professor Sauermann.**

*You spent nearly ten years in the US, at Stanford, Princeton and Boston. What led you to come to the University of Bonn?**Quality of life in Germany is much higher than in the US; that’s why I wanted to return. You always have to drive to the supermarket and everywhere - it gets to be a real drag. Bonn is a right-sized city to me, where you have everything you need right there, nothing is too far away. It’s a beautiful, green city as well. That’s also important for my two daughters, who are two and four years old. I had multiple options where I could go in Germany, but the University of Bonn is really an exceptional place for mathematics, and they made me the best offer.*

*What things are better in Bonn than at other German universities?**Mathematics is more of a focus here than at other universities, and mathematics in Bonn has more resources, and more and better students. Many students come here to study mathematics, from all over Europe and around the world. This, as well as the contact with the other researchers at the Hausdorff Center for Mathematics, leads to new ideas and research connections, and a fantastic pool for recruiting PhD students.*

*What is it about mathematics that you find fascinating?**My work is in the field of probabilistic combinatorics. I think it's fascinating to address combinatorial problems applying methods from probability theory. Sometimes I utilize algebraic techniques as well. I’m also interested in combining these methods, which can lead to new approaches.*

*How have you come up with your best ideas for new mathematical challenges?**Sometimes I get ideas just sitting at my desk with paper and pencil, the ‘classic’ way. When I get excited about a problem, it keeps circulating around and around in my head. It happens to be a very productive time for me when I’m putting our daughters to bed. At first they are doing nonsense, but then they quieten down ... and that’s when ideas come to me for the mathematics problems I'm working on.*

*As a mathematician, you probably are thinking about problems like that all the time. How do you manage to power down in the evening?**My day has a natural structure: In the morning I drop off the children in daycare, then I have time to do mathematics in the office. I pick the kids up again at 4:30 pm, and between then and their bedtime my brain gets a break from mathematics. I think it’s basically the same way as for most other professions.*

*You have been working at the Hausdorff Center for Mathematics for a few weeks now. Do you have a favorite spot here where you like to go? **Outside the Math Center there’s a very pretty lawn where I've always wanted to work, read papers and so on. But the last few days were so rainy, and today it’s far too hot to go out there. But I am looking forward to trying that spot out.*

*Where do you like to go on lunch break?**Thus far I have been going to the canteen on the Poppelsdorf Campus, which is right around the corner here. I’m wondering how much variety there will be in the menu. Once I get my working group formed, we can all go to lunch together, which is great for informal community building.*

*In your experience, do women have a harder time in the field of mathematics than men?**I haven't had any problematic experiences myself. That probably depends on the environment you’re working in. I think the low percentage of women in mathematics is due more to larger societal structures than to individuals making life difficult for women. Having children myself has given me a certain perspective on this subject. Common stereotypes influence children from an early age: technology is for boys; girls are good at drawing. These stereotypes affect girls and young women in their self-confidence and influence the interests they develop.*

*If your job were to advertise the study of math, what would your approach be?**Studying math is just great! It’s a lot more fun than math at high school. There, the focus is on calculation recipes, and students often do not learn about the reasoning behind the calculation steps. The approach is similar to baking a cake: You don't necessarily have to understand what the baking powder does. But what is the point if the math class does not teach what is behind all the calculations? Studying math at university is very different. Here the focus is on understanding mathematical structures.*

*Have your husband and your two daughters gotten settled in well here in Bonn?**My daughters acclimated to their new life pretty quickly. They are not having any linguistic problems either, because I always spoke to them in German. My husband, who is Canadian and is also a mathematician, really likes it here as well.*

*Now things have come full circle, having done your bachelor's in Bonn in 2014 ... and now you’re back. What things have changed in the meantime?**The Poppelsdorf canteen has changed a lot: it has been completely renovated. But the Math Center building looks exactly like it used to. I am also excited to see the new lecture hall center on Poppelsdorf Campus once lectures start up again. *