His research, as well as much of his teaching, concerns number theory and formalization of mathematics:
"My main field of research is number theory, in which I mostly focus on explicitly resolving Diophantine equations. These are multivariate polynomial equations whose coefficients and unknowns must be integers, or sometimes rational numbers. Diophantine equations form one of the oldest branches of mathematics, but the subject is more alive than ever before. They play a central role in modern number theory, with many connections to other branches of mathematics and beyond. A few years after joining VU Amsterdam, I also entered the research area of (computer assisted) formalization of mathematics. This is an interdisciplinary area between mathematics and computer science, which is quickly evolving and promising to provide indispensable tools for future mathematicians, computer scientists, and the like. I am interested in the subject as a whole, but naturally, my focus within is on formalization of number theory."