The rule doesn't mean that digits in shaded cells will repeat. The digit in a shaded cell is irrelevant for that cell, it means (at least) two cells around that cell will have repeating digits. So in the 6x6 that is forced to be in a shaded cell but the way to look at it in there is, for R2C3, R2C4 and R3C3 are repeating among the 4 cells around it, so R2C3 is shaded. Since R2C3 and R3C4 are also repeating, R2C4 and R3C3 are shaded because for both of those cells, a digit is repeating in the 4 cells around them.

Explaining with a diagram. In the image at the right, the cell X has 4 orthogonal neighbours. They are marked as a,b,c,d. As you can see X shares an edge (side) with each of the four. Now the rule of the Sudoku : If the cell X is white, a, b, c & d must be all different. If the cell X is shaded, then there must be some repetition among a,b,c,d (i.e. At least one of a = b or a =d or c = b or c =d must be true)

Thanks a lot Prasanna and Deb Mohanty. Your explanations have helped a lot, specially with the diagram.
Just to confirm " a can never be = c" and " b can never be = d"

You are right. We will be violating Classic Sudoku rules if a =c or if b = d.

Oops just didnt thought over it, was so confused on the entire things. Anyways thanks a lot :)

I am not able to get a start for the repeated neighbours sudoku (6*6). Can anyone plz help?

See the image above and ask yourself this - if X is shaded, to accommodate any combination of repeating letters, wouldn't you need another shaded cell nearby, considering that white cells cannot have repeating neighbours?

Yeah done. Thanks

In touchy sudoku, is it just clue digits that require a consecutive neighbor? Or is it every digit in the full solution?

Every digit in the full solution.

I was posting a pic for reference...but the file size was big

How well did the variants represent the theme of the test ?	representation could have been better
What was your opinion of the distribution of easy/hard puzzles?	Just right
What did you think about the puzzle quality of the test?	Very nice
Of the puzzles you solved/attempted, how well did the point values reflect the difficulty?	Most puzzles were worth the right amount

How well did the variants represent the theme of the test ?	variations represented the theme well
What was your opinion of the distribution of easy/hard puzzles?	Too many hard puzzles
What did you think about the puzzle quality of the test?	Very nice
Of the puzzles you solved/attempted, how well did the point values reflect the difficulty?	Most puzzles were worth the right amount

That was an absolute feast of sudokus! Thanks Aditi and Prasanna for authoring a wonderful test.The sudokus were hard and testing.If I may add,this test should be a bit harsh on the beginners but it really must provide an excellent challenge to the veteran solvers.I anticipate the number of solvers who complete the test to be much lesser than the previous episode.Overall, this can be treated as an opportunity for the beginners to get some new ideas and understand more about tough sudokus in general.
Repeated Neighbours was the hardest of the lot followed by Touchy and they certainly justified their points worth.I find it difficult to choose my favourites as I enjoyed solving almost all.However,the standouts for me were Renban(7),Quadruple(11) and Thermo(9) in that order .Good to see young Aditi entering into the fray of Indian authors.This bodes well for the future.

---Kishore---

How well did the variants represent the theme of the test ?	variations represented the theme well
What was your opinion of the distribution of easy/hard puzzles?	Just right
What did you think about the puzzle quality of the test?	Fairly Nice
Of the puzzles you solved/attempted, how well did the point values reflect the difficulty?	Most puzzles were worth the right amount

How well did the variants represent the theme of the test ?	variations represented the theme well
What was your opinion of the distribution of easy/hard puzzles?	Just right
What did you think about the puzzle quality of the test?	Very nice
Of the puzzles you solved/attempted, how well did the point values reflect the difficulty?	Most puzzles were worth the right amount

Lovely set of sudokus!
I really liked the new gimmick on Quadruple Sudoku.
Am I the only one who found the second Repeated Neighbours very tough?
I thought that puzzle was rather unfairly more difficult than the second-hardest one in the lot.
There's people with 17/18 but have very good times.

It does seem to have been very tough going by the timings. I had both Deb and Rishi solve that one and had no issues (Rishi actually took longer on Touchy and still had a total testing time which was around 2 min more than his time for R1), but I guess it is a big strength for both of them. You need to get three pairs of repeating digits in each quadrant. I think it is possible to get those just by looking at the grid, but Jan Zverina says he missed the middle one and Tiit also says he missed the middle one for a while. So it might just be that. Was your experience of difficulty somewhere else?

I just took long to get the insight that there has to be three pairs in each 'region'.
Even knowing that, I ended up bifurcating to get my answer.
Nonetheless, it was a beautiful puzzle, requiring leaps of insight, one I would be happy with if I had wrote it :)

How well did the variants represent the theme of the test ?	representation could have been better
What was your opinion of the distribution of easy/hard puzzles?	Just right
What did you think about the puzzle quality of the test?	Fairly Nice
Of the puzzles you solved/attempted, how well did the point values reflect the difficulty?	Most puzzles were worth the right amount

How well did the variants represent the theme of the test ?	variations represented the theme well
What was your opinion of the distribution of easy/hard puzzles?	Too many easy puzzles
What did you think about the puzzle quality of the test?	Very nice
Of the puzzles you solved/attempted, how well did the point values reflect the difficulty?	Most puzzles were worth the right amount

How well did the variants represent the theme of the test ?	variations represented the theme well
What was your opinion of the distribution of easy/hard puzzles?	Just right
What did you think about the puzzle quality of the test?	Very nice
Of the puzzles you solved/attempted, how well did the point values reflect the difficulty?	Many puzzles were worth too much or too little

Feedback tool hangs for me (flash).
Good variations for the theme.
I personally liked the easy/hard distributiion -- probably too many hard ones for beginners though.
Excellent puzzle quality! Some real delights.
Point values seems pretty fair.

Prasanna's class stamped all over, including IB

How well did the variants represent the theme of the test ?	variations represented the theme well
What was your opinion of the distribution of easy/hard puzzles?	Too many hard puzzles
What did you think about the puzzle quality of the test?	Very nice
Of the puzzles you solved/attempted, how well did the point values reflect the difficulty?	Most puzzles were worth the right amount

How well did the variants represent the theme of the test ?	representation could have been better
What was your opinion of the distribution of easy/hard puzzles?	Too many hard puzzles
What did you think about the puzzle quality of the test?	Very nice
Of the puzzles you solved/attempted, how well did the point values reflect the difficulty?	Most puzzles were worth the right amount

In my opinion, the neighbours theme sees on direct relationships between two orthogonal connected cells. Renban and Quadruple are a little bit off this theme. But: I enjoyed the test very much. Really nice aesthetics and solving routes. Maybe a bit on the hard side for beginners, exactly the right difficulty level for me! Thanks a lot!