Not just challenging; I don't have any clue on how to go about doing that either! What I used was this: solving four wing pieces (the UF dedge and two other pieces), five centre pieces, and one corner piece; this was done with two small pruning tables (~4-5 million entries). I then multiplied the resulting pruning value by 2, which makes it almost certainly not optimal, and filtered the solutions (which can have up to 16 unsolved wings and 17 unsolved centres) for those that had only fixed points and 3-cycles.
Now I'm running a full optimal search (i.e. solving only the UF dedge, no restrictions on other pieces), but it's only finished exploring 25 moves so far. (The code is… not fast.) Edit: finished searching up to 27 moves now; still hasn't found anything. Edit 2: oops, found a bug—it was searching something completely different. Disregard this whole paragraph!
Now I'm running a full optimal search (i.e. solving only the UF dedge, no restrictions on other pieces), but it's only finished exploring 25 moves so far. (The code is… not fast.) Edit: finished searching up to 27 moves now; still hasn't found anything. Edit 2: oops, found a bug—it was searching something completely different. Disregard this whole paragraph!
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