Oscar wrote:
And without using Jean-Christophe location of the UR Type1, I was unable to find the XY-chain
A UR-1 is not necessary for solving 4D. Personally I use whatever techniques makes me solve a Sudoku, and do not feel obliged to use only what a logical solver needed, especially since the solver applies the techniques in a specified sequence. If you use Chains you can avoid most other techniques except Almost Locked Sets, which only and always are required to solve the Wizard editions. Finding a Chain in a Vanilla Sudoku is often hard, so finding one in a 10 grid CS is of course "10 times harder".
This weeks Clueless Special Master edition should be an interesting one. The hardest technique required is Naked/Hidden subsets, but there are lots of them and very many Intersections. The required techniques for the Guru edition reads like a small horror story. Here the required techniques according to JSudoku 1.3b1:
C) Master (81 Intersections, 9 Naked Pairs, 9 Naked Triplets, 5 Naked Quads, 1 Hidden Pair).
D) Guru (72 Intersections, 9 Naked Pairs, 4 Naked Triplets, 1 Naked Quad, 2 Hidden Pairs, 2 Turbot Fishes, 1 Finned X-Wing, 1 Finned Swordfish, 1 Grouped TF, 1 Y-Wing, 4 XY-X-Chains up to 3 links).
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