Is this the reason why Rubik has gone into hiding? I haven't seen any
puzzle from him after this set of 4 released in 1990/1991.
Hm, didn't "Square-1" come out later than the Tangles?
Regarding solving the Tangle, I forgot one other minor optimisation: When
my program is picking a corner piece other than the first, it requires that
the piece "number" be less than or equal to that of the first corner. I.e.,
it refuses to search for solutions that are rotations of other solutions.
I've modified my program to try the 10x10, but indeed, it's taking a long
time. (Current estimate is it will take over a year to finish.) I suspect
that fact that pieces aren't "used up" as fast -- i.e., since there's at
least four of any given piece, there will usually be at least one of whatever
you're looking for for quite a ways down the search tree -- makes this