Automorphisms of the Rado meet-tree

Abstract

We prove that the group of automorphisms of the generic meet-tree expansion of an infinite non-unary free Fraïssé limit over a finite relational language is simple. As a prototypical case, the group of automorphisms of the Rado meet-tree (i.e. the Fraïssé limit of finite graphs which are also meet-trees) is simple.