The diameter of associahedra

It is proven here that the diameter of the d  -dimensional associahedron is 2d−4$2d-4$ when d is greater than 9. Two maximally distant vertices of this polytope are explicitly described as triangulations of a convex polygon, and their distance is obtained using combinatorial arguments. This settles two problems posed about twenty-five years ago by Daniel Sleator, Robert Tarjan, and William Thurston.