I remember these from when I was a kid. There was one with a bunch of numbers in it, with the even numbers one color and the odd numbers another color. 1 through 15; the instructions said that there were certain things you could NOT do, though I cannot remember them after all these years.

But it was something like end up with all of the odd numbers in order above all the even numbers in order:

1 3 5 7
9 11 13 15
2 4 6 8
10 12 14 .

Anyway. You could NOT get them to move into the configuration, though you could take the puzzle apart and put them into that configuration.

But did this mean you could not get it back into the base configuration:

1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 ?

In the years since then, I have read a mathematical proof as to why you could not go from one configuration to the other, but due to advancing years I cannot (what the HELL are we talking about???)


TEd