# Colloquium: Local Constraint Solving — How to Colour Without Looking (Much)

- Date:
- Location: Ångströmlaboratoriet, Lägerhyddsvägen 1
- Lecturer: Alexander Holroyd
- Contact person: Thomas Kragh
- Seminarium

How can individuals cooperate to satisfy local constraints without a central authority? Individuals can make random choices and communicate with each other, but all must follow the same procedure. How small can we make the “coding radius” — the distance to which an individual must communicate? In the setting of the integer line Z, there is a surprising universal answer that applies to every non-trivial constraint problem. In d-dimensional Euclidean space, answers are available for the key case of proper colouring; it turns out that there is a huge difference between 3 and 4 colours. Finally, I'll mention how changing the question slightly has led to the discovery of an amazing mathematical object that seemingly has no right to exist.