1. Minimization problem;Bellman;Bull. Am. Math. Soc.,1956
2. Million-buck problems;Williams;Math. Intell.,2002
3. Lost in a forest;Finch;Am. Math. Mon.,2004
4. Hyperbolic dovetailing;Kirkpatrick,2009
5. Tomorrow's Math; Unsolved Problems for the Amateur;Ogilvy,1972