Hm. Well, I split up the 10x10 Tangle exhaustive search and ran it on
several machines over Christmas break, getting the 90 days of compute
time done in about 10.
And turned up no solutions.
There could of course be a bug in my program, but the same code with
minor changes finds the same solutions as others have found for the 5x5.
I also tried adding some extra tiles for the 10x10, and it began finding
solutions okay. I did doublecheck that the 100 tiles matched the info
posted to Cube-Lovers re which tiles are duplicated in the four 5x5s;
I have no way of checking whether that info was correct.
Has anyone out there ever heard definitely that someone has found a
solution to the 10x10? Is it possible that the makers of Tangle (Matchbox,
using Rubik's name under license) merely claimed that such a solution
exists, without actually verifying it? (Seems pretty sleazy if so,
but then, having Tangles 2-4 be merely color permutations of #1 is
pretty weak in the first place.)