When every cell a row or column still has open to a digit lies inside one box, the line's copy of that digit is in that box, so every other cell of the box loses it. Two cells make a claiming pair, three make a claiming triple.
How to spot it
Pick a row or a column and a digit it is still missing, and ask where that digit can go along the line. It is the question the hidden single asks of a line. When the answer is one cell, you have a placement. When it is two or three cells, look at which box they are in.
A line crosses three boxes. If every cell still open to the digit sits in the same one of them, the line has settled which box its copy goes in without settling which cell. That box can hold the digit only once, and the line is going to use that one. So every cell of the box off the line loses the digit.
Two cells make a claiming pair and three make a claiming triple. There is no claiming quad, because a line shares only three cells with any box. Other guides call the move box/line reduction, or locked candidates type 2.
Ask row two where the 3 can go
Row two has four empty cells. The second cannot take a 3, because column two has one at the bottom. The fourth cannot either, because column four has a 3 in row six. That leaves the last two cells of the row.
Both cells are in box three
One of those two cells will hold row two's 3. You cannot tell which yet, and you do not need to. Both are in box three, so wherever it lands, box three's 3 is in row two.
Clear the rest of the box
Box three can hold one 3, and row two is going to supply it. So no cell of the box outside row two can be a 3, whatever else it shows. Five cells still carry a 3: two in the box's top row and all three in its bottom row. All five lose it. Nothing in row two changes.
Read what the strike left behind
The top-right cell of box three was showing 2 and 3. Without the 3 it has one candidate left, so it is a 2: a naked single. Before the strike this grid had no single of either kind anywhere. The claim is what moved it.
Every mark on the line counts
Claiming is about one digit on one line. Box three offers a second case that looks like the first and is not.
Take column seven, the left column of box three, and its 6. Two of the column's cells that can take a 6 are in box three, at the top and the bottom of the box. A third is further down, in row seven, which is in box nine. So column seven has not settled a box for its 6. Strike box three's other 6s anyway and they come out of the centre cell and the bottom-middle cell. On this grid the centre cell of box three is where the 6 belongs, so that strike leaves the puzzle with no solution at all.
Before you strike, find the digit in every empty cell of the line, including the ones in the other two boxes.
Both of row two's 3s are in box three. The rest of box three loses its 3s.
A third 6 sits in row seven, in box nine. Box three keeps its 6s.
Two cells or three
A claiming triple is the same move with three cells. The digit's homes on the line fill the whole stretch where the line runs through one box, and the argument does not change: the line's copy is in that box, so the rest of the box loses it.
Row seven has one. Its 3 can only go in its last three cells, the top row of box nine. The first and third cells of the row are shut by the 3 in box seven, and the sixth cell by the 3 in box eight. So row seven's 3 is in box nine. Box nine has nothing to give up, though. Rows eight and nine each hold a 3 already, so none of the box's other five empty cells carries one. This triple is real and changes nothing, so look at the box before you count on a result. The question at the end of this page has a triple that does remove something.
The strikes land inside the box, off the line. If you find yourself removing a digit from the line outside the box, you are running the move the other way, and that is pointing. Both run on the same three cells, the ones a box shares with a line. If either of the two can only put a digit there, the other has to put it there too.
Where this sits on the path
Claiming places nothing. Like pointing, it only removes candidates and leaves the placing to the singles. On the grid above the strike placed nothing by itself. It turned the top-right cell of box three into a single.
That 2 was out of reach of the last possible number. The cell's row, column and box rule out seven digits between them. The eighth, the 3, was ruled out by the claim, and no placed digit shows that.
The subsets chapter comes next on the path. A naked pair ties two digits to two cells, and a hidden pair ties them from the digits' side. Pointing and claiming are the one-digit version of that idea: a digit tied to the three cells where a line and a box cross.
Column two runs through box one. Which candidates can you strike from the first cell of row three?
Take each digit column two is still missing and ask the column where that digit can go.
Итог
- Ищите
- A row or column where every cell still open to one digit is inside the same box.
- Область
- Starts in a row or column and removes inside a box. Two cells make a pair, three make a triple.
- Результат
- The digit comes out of every cell of that box off the line. Nothing on the line changes.
- Признак
- Ask a line where a digit can go. Two or three answers in one box, and none in the other two boxes the line crosses.
- Если не сработало
- If one more cell of the line carries the digit in another box, the line has not settled a box and nothing can be struck. Try the next digit or the next line. If no line claims and no box points, look for a naked pair.