# Pure Maths Colloquium: Alan Logan

This talk is part of the Pure Maths Colloquium at the University of St Andrews. Check out our upcoming talks at https://theran.lt/pure-colloquium/.

 Where: Zoom 840 9694 7894 When: Sep 30 2021 @ 16.00 Video: Link (internal)
 Speaker: Alan Logan Heriot-Watt University Title: Equalisers of free group homomorphisms

The equaliser of a pair of maps $$g, h:S\to T$$ is the set of points where they agree. Equalisers of free monoid homomorphisms have been studied in Computer Science since the 1940s, when Post proved that their triviality is undecidable (this is Post’s Correspondence Problem). In this talk, I’ll explain links between equalisers of free group homomorphisms and certain long-standing problems in (Geometric) Group Theory, and explain how we can use “Stallings’ foldings”, or “Stallings’ automata”, to study these objects.

Based on joint work with Laura Ciobanu.