See "Picture-Hanging Puzzles" by Erik Demaine et al. ([arXiv link][1]):
<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
![Rope/Kids][2]


  [1]: http://arxiv.org/abs/1203.3602
  [2]: http://cs.smith.edu/~orourke/MathOverflow/ErikRopeTrickKids.png