A short story by O. Henry which offers a classic example of a CyclicDependence? problem.
It's online at http://www.auburn.edu/~vestmon/Gift_of_the_Magi.html.
For the interested, a plot summary is below, after the spoiler space.
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A poor couple is desperately in love, and each spouse wants to buy the other one special gift for Christmas. The wife prizes her long, silky hair, while the husband prizes his expensive pocketwatch. The wife cuts her hair and sells it, using the money to buy her husband a beautiful gold chain for his pocketwatch. Meanwhile, the husband sells his beloved pocketwatch and uses the money to buy his wife a beautiful comb for her long tresses of hair. The story finishes: