Alphachris on 26 April 2012
If you "rewind" and the robber changes his decision, you just proved that there is more than one possible solution.
But if you rewind 1.000.000 times and he always robbed... that would still not be a proof that he couldn't decide differently the next try. You just showed that the chances for an other solution are very small.
You just can't prove non-existence with logic.
