Chapter 14.1, Problem 22E

In Exercises 21-22, a mail carrier is to walk the streets of the neighborhood shown in Exercises 19 and 20, respectively. Unlike the security guard the mail carrier must walk down each street with houses on both sides twice, covering each side separately. Draw a graph that models the neighborhood for the ma it carrier. Use vertices to represent the street intersections and comers. Use edges to represent the streets the mad carrier needs to walk, with one edge for streets covered once and two edges for streets covered twice.

See the figure for Exercise 20.