This diagram represents the geographic relation of some cities in the Puget Sound region of Washington state. A line (possibly a crooked line) connecting two cities means you can reach one from the other without passing through any of the other cities.
Bremerton ------------- Seattle
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Gig Harbor -------------Tacoma
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+------ Olympia ------+
Define a Scheme variable named puget-routes to encode
this diagram. Represent city names by (double-quoted) strings so we
can easily represent cities whose names have more than one word:
"Seattle", "Gig Harbor" etc. Represent the
diagram as a list of lists. The car of each list is the
name of a city and the cdr of each list is a list of all
the cities that can be reached from the first city.