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How to play XV Sudoku
XV sudoku marks some pairs of neighboring cells with an X or a V. The two digits across an X add up to 10 and the two across a V add up to 5, the Roman numerals.
A V can only be 1 and 4 or 2 and 3, so it pins down cells fast. An X can't hold a 5 (that would need two 5s side by side). With the negative rule, a missing letter is a clue as well.
At a glance
- An X joins two digits that add up to 10.
- A V joins two digits that add up to 5.
- 5 can never sit on an X or a V.
- Only 1, 2, 3 and 4 can sit on a V.
XV pairs chart
Every digit and its only partner across an X or a V. Each digit has exactly one X partner, which makes X clues very tight once a digit is known.
| Digit | Across an X (sum 10) | Across a V (sum 5) |
|---|---|---|
| 1 | 123456789 | 123456789 |
| 2 | 123456789 | 123456789 |
| 3 | 123456789 | 123456789 |
| 4 | 123456789 | 123456789 |
| 5 | 123456789none | 123456789none |
| 6 | 123456789 | 123456789none |
| 7 | 123456789 | 123456789none |
| 8 | 123456789 | 123456789none |
| 9 | 123456789 | 123456789none |
X pairs: 1-9, 2-8, 3-7, 4-6. V pairs: 1-4, 2-3. 5 fits neither.
How to start a XV sudoku
Fill the V cells
A V is 1 + 4 or 2 + 3, so its two cells are low digits only. Pencil 1 to 4 in every V cell.
Take 5 off every X
5 + 5 is the only way to make 10 with a 5, and two neighbors share a row or column. No X or V cell is ever 5.
Use the one-partner rule
Across an X, each digit has exactly one partner: 1-9, 2-8, 3-7, 4-6. Know one cell and you know the other.
Squeeze with the negative rule
When all X's and V's are given, no other neighbors add to 5 or 10. A cell between two unmarked neighbors loses a lot of options.
Check boxes for pairs
Two V's in the same box must be 1 + 4 and 2 + 3, one each, so the rest of that box can't hold 1, 2, 3 or 4.
Common mistakes
Putting a 5 on an X
It would need another 5 next to it, in the same row or column.
Mixing up X and V
X is the Roman numeral 10, V is 5. If in doubt, V is the small one.
Assuming the negative rule
Only some puzzles say all X's and V's are given. Check the rules panel.
Five levels, no guessing
Every puzzle has one solution, proved when it is set, and our solver finishes it by logic alone. The level is the hardest step the solve needs. Here is what each level asks of a XV puzzle:
- EasyClearing digits that can't sit on an X or a V, then singles.Play Easy
- MediumThe pairs each X and V allow, plus pointing pairs.Play Medium
- HardThe negative rule (no X or V means no 5 or 10), pairs and triples.Play Hard
- ExpertX-Wings, Skyscrapers and wings on top of the X's and V's.Play Expert
- FiendishChains and coloring, and testing every way the clues can be filled.Play Fiendish
The daily variant rotates through 11 kinds, so a XV daily comes round about every 11 days. Past dailies
Hand-set XV puzzles
Our levels are a good start. For more, Explore has 338 XV puzzles made by people, from Logic Masters and Cracking the Cryptic. A few of the most popular:
Soapbox Raceby wuc
Sandwichby burgermason
Erica 2by SennyK
GAS whispersby brtmns
Colorado 11by Florian Wortmann
Quintuple Qwednesdayby EmpyClaw
Empty clues, equal rulesby fractalminding
Lil Loco Puzzle 1 The Euroby RailManSetters with the most XV puzzles:
- NotSoMagnifique 22
- pagedo 18
- Will Power 10
- SennyK 9
- gUBBLOR 8
- starwarigami 8
- lgastako 7
- James Kopp 7
- meggen033 6
- Scojo 5
Often combined with:
Questions
Which digits can be on a V?
Only 1, 2, 3 and 4, as the pairs 1 + 4 and 2 + 3.
Why can't 5 go on an X?
The other cell would also need to be 5, and the two cells share a row or column.
What does 'all XVs are given' mean?
No two neighbors without a letter sum to 5 or 10. It often removes more candidates than the letters themselves.
Which pairs can go on an X?
1 and 9, 2 and 8, 3 and 7, 4 and 6. Each digit except 5 has exactly one X partner.
Is XV sudoku the same as kropki?
No, but they're cousins: both put clues on the border between two cells. Kropki dots are about differences and doubles, XV clues about sums. Try kropki sudoku next.
Where can I learn XV logic?
The XV lesson walks through the rule and the negative constraint with animated examples.
More ways to play
Classic Sudoku1 to 9 in every row, column and boxKiller SudokuCages that add upThermo SudokuDigits climb from the bulbArrow SudokuThe arrow sums to its circleKropki SudokuWhite dots, black dotsSandwich SudokuSum between the 1 and the 9German Whispers SudokuNeighbors differ by 5 or moreDiagonal SudokuBoth diagonals hold 1 to 9Anti-Knight SudokuNo repeat a knight's move apartAnti-King SudokuTouching cells never repeat