William Rowan Hamilton invented a puzzle that was manufactured and sold in 1857. On a graph, a Hamiltonian path is one that visits each vertex once without revisiting an edge. See the entry at [url=https://www.puzzlemuseum.com/month/picm02/200207icosian.htm]the Puzzle Museum[/url].[br][br]Try Hamilton's puzzle here. Click on an edge to light it up, and try to make a path to visit each vertex. If you need to begin again, use the reset icon. Does it matter where you start?[br][br]The puzzle is named for this graph being isomorphic to the vertices and edges on an icosahedron.