August 2011
Intermediate to advanced
261 pages
3h 41m
English

The reason you may not have been able to solve the problem is that unconsciously your mind imposed a framework around the nine dots. You have to go beyond that invisible box. From this problem, which I introduced in 1969, comes the phrase ‘Think outside the box!’
Again, ask yourself the reason you couldn't solve it. Were you making an assumption or imposing a constraint that the puzzle must be solved on one plane or in two dimensions?
Breaking out of the two-dimensional unconscious assumption and into three dimensions gives the most elegant solution:
Move the bottom coin up and ...
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