enxio27 wrote:
Now I see it! I must have taken a harder path using all five of those highlighted cells to eliminate the 5 in r4c1.
You can use a 4 cell chain (XY-X-Chain I think, getting a bit rusty so I have to think it over) r4c8 -> r6c8 -> r6c4 -> r4c5 to prove that r4c1 <> 5.
Here a Y-Wing, which proves that r4c1 <> 5
enxio27 wrote:
Out of curiosity, do I really need the r4c58 to eliminate the 5 in r6c4?
If you have any suggestions on how to eliminate the 5 in r6c4 without using r4c58, I am all ears!
enxio27 wrote:
BTW, did you go back and delete part of your above post? I could have sworn there was some description of 2-string kite and another technique being special cases of the Y-wing, but now it's gone.
YES, I did go back and delete part of my above post. I wrote that Two-String Kite and Skyscraper are special cases of the general Y-Wing. This is of course absolute rubbish. As I said above, getting a bit rusty from not having solved sudokus in a while.