## Lecturer in the Spotlight: Sonja Cox

### 'What I love about maths: you get a puzzle, you have some tools, and then you have to solve it’

Sonja Cox (KdVI) is researcher in the research group Stochastics. As a lecturer, she teaches first-year Mathematics Bachelor's students, as well as in the national MasterMath programme and at AUC.

When Sonja Cox was a Master's herself (at Delft University of Technology), she was often one of only three or four students at the lectures. Since then, mathematical Master's degree programmes in the Netherlands have combined some of their Master's courses in the national MasterMath programme. 'Even aside from larger class size, the concept is wonderful, because the courses can now be taught by the specialists from all universities.'

At MasterMath, she teaches a core course designed to ensure that all students are armed with the same knowledge to obtain a Master's in probability theory. A challenge for Cox: 'During the first six weeks, they get a crash course in measure theory. And it is the same every year: half of the class is bored because they already know the material, while the other half can hardly keep up because it is all new. But after that we can really get into the fun stuff.'

### Faith

By 'fun stuff', Cox means probability theory. Stochastics 1, which she teaches to first-year Bachelor's students, gives them a first taste. And that, too, comes with a challenge. Cox explains: 'Modern probability theory relies heavily on analysis and measure theory, which at that point is still new for them.' So, often, she has to ask students to take it on faith: 'OK, guys. You will learn about it this later. For now, just trust me: it works like this.' Difficult, but also understandable: 'It is a good idea to expose students to probability theory in their first year because it is such a fundamental part of Mathematics.'

### Finding the tools yourself

Above all, it is incredibly important that students get to work on the exercises themselves, says Cox. 'That is what I love about maths: you are handed some tools and you get a puzzle. Then you have to solve it with the available tools.'

Whereas these tools are handed to students at first, eventually students are expected to find them on their own. 'That is where the programme ideally takes them in five years. New students often assume that 'if there is anything I need to know, my lecturer will tell me,' but that attitude should gradually evolve into, 'If I want to solve this, I will have to look there or there for the tool I need do it.’ That is one of my favourite things about teaching: when you see that students start to get it, that they enjoy that and then they want to learn even more.' This makes it a real challenge for Cox not to overwhelm them. 'I love it so much when they’re asking questions, that I tend to want to tell them too much all at once. So I have to pace myself sometimes.'

### Choosing Mathematics

Given her passion for the subject, it’s surprising to learn Cox basically chose Mathematics through a process of elimination. ‘I found it extremely hard to choose. Law seemed interesting, but I thought the programme was too large-scale. Studying Physics was a touchy subject because my mother had wanted to do that, but was not allowed to. Philosophy did not provide me clear enough answers and you had to do so much practical lab training with Chemistry... With everything I knock over when cooking at home, that did not seem wise.' That left Mathematics, and not only because the 'practical' programmes did not excite her: 'It seemed challenging and I liked the small scale. And yes, obviously, I liked solving puzzles.'