Puzzle 17- The Wandering Toad |

Mr. Toad
lives on a vertex of a 3-regular planar graph. He decides to take a walk
along the edges of the graph. He has no sense of direction but he can tell
left from right. He decides that he will alternately take the left edge
and then the right edge when he comes to the next vertex. Show that he will
he eventually get back home.