The Antidot
(Published on 9. September 2026, 00:00 by Fool on Hill)
This idea for this puzzle was inspired by Billybeth's excellent puzzle I See No Dots, which left me wondering whether a German Whisper puzzle could be disambiguated by a single negative constraint.
I have set several puzzles with German Whisper clues which are disambiguated by a single clue: I have tended to use black dots for the purpose. This puzzle has a single German Whisper line, with no black dots given and a negative constraint on black dots. No adjacent pair of digits has one digit twice the other.
Opinions on difficulty have varied somewhat amongst testers. I have started it at 4/5, but a few solvers are likely to find it rather easier. The title arose because a tester who commented on the puzzle when it was called "What on earth is that" said that it was easy to forget a negative constraint.
Puzzle rules
Normal Sudoku rules apply.
On a green line adjacent digits must differ by at least 5 (standard German whisper)
Where digits are separated by a black dot, one is twice the other. All black dots are given.
Play in SudokuPad: The Antidot
Solution code: Column 2
Comments
yesterday, 18:19 by apete
That was lovely. Well set. Enjoyable flow. Thank you.
on 10. September 2026, 12:47 by Arheus
I liked it. The negative constraint is powerful enough so that, with a bit of attention and scanning, this is a 3* puzzle.
on 9. September 2026, 23:04 by brskri
Fantastic use of the negative constraint! This was difficult, but doable. As with other negative constraint puzzles, good scanning is helpful to completing faster. I especially like that this gives you some easier bits to start out with so it's not daunting from the start.
on 9. September 2026, 19:28 by GeorgeTheToad2
Well constructed Fool On Hill, hopefully Simon or Mark will make that number 6 on your feature list. Took me almost an hour.
on 9. September 2026, 14:51 by Rollo
Brilliant
on 9. September 2026, 10:38 by Snookerfan
Very nice! The negative constraint is so powerful, that I gave it a 3 sta difficulty. Thanks
on 9. September 2026, 04:02 by BigHead
Wonderful puzzle, thank you!
