This is the Harborth graph, the simplest known planar graph in which all the edges are the same length and every vertex has exactly four neighbours Posted on 2020/11/15 by Carl Robitaille This is the Harborth graph, the simplest known planar graph in which all the edges are the same length and every vertex has exactly four neighbours. pic.twitter.com/cvwK6W2ymD— .robin. (@robinhouston) November 15, 2020