Flip graphs of coloured triangulations of convex polygons

Abstract

A triangulation of a polygon is a subdivision of it into triangles, using diagonals between its vertices. Two different triangulations of a polygon can be related by a sequence of flips: a flip replaces a diagonal by the unique other diagonal in the quadrilateral it defines. In this paper, we study coloured triangulations and coloured flips. In this more general situation, it is no longer true that any two triangulations can be linked by a sequence of (coloured) flips. In this paper, we study the connected components of the coloured flip graphs of triangulations. The motivation for this is a result of Gravier and Payan proving that the Four-Colour Theorem is equivalent to a property of the flip graph of 2-coloured triangulations: that any two triangulations can be 2-coloured in such a way that they belong to the same connected component of the 2-coloured flip graph.