隐性唯一 Hidden Singles
定义1 宫内隐性唯一 Hidden Singles in Box
如果某个宫内，某个数字只能填在一个单元格内，这里就是宫内隐性唯一。绝大多数题目中的绝大多数步骤都是宫内隐性唯一，这个技巧是基本功里的基础。
If a number can only be in one cell in a Box, that's a Hidden Single in that Box. Hidden Single in Box is the most common step in most common puzzles, it's the basic of the basic.
◆单次排除 Eliminate for once
有的时候，我们只需要画出一条排除线。
Sometimes we just need only one eliminate line.
◆多次排除 Eliminate for several times
在更多的情况下，我们需要更多的步骤，也有时会有干扰数字。
In most situation, we need more than once step. Sometimes, there may be interference numbers.
定义2 行列隐性唯一 Hidden Singles in Row/Column
如果某个行列内，某个数字只能填在一个单元格内，这里就是行列隐性唯一。这种隐性唯一会比宫内的更为隐蔽。
If a number can only be in one cell in a Row/Column, that's a Hidden Single in that Row/Column. Hidden Singles in Row/Column will be more covert.
定义3 基本功 Basic Techniques
显性唯一和隐性唯一统称基本功，其余的所有技巧都算是辅助技巧。如果我们想要获取下一步的具体数字，我们必须寻找显性或隐性唯一。
Naked Singles and Hidden Singles form Basic Techniques. All other techniques are auxiliary means. If we want to get a next sure number, we must find Naked or Hidden Singles.
定义4 最后一数Last Digit
在N阶数独内，每个数字出现N次。如果一个数字出现了N-1次，我们找到最后一个的步骤就是最后一数。
In a NxN sudoku, each number will appear N times. If a number appear N-1 time, and we find the last one, that's a Last Digit.
如果我们寻找到数字A，我们应当去寻找尽可能多的A。在绝大多数情况下我们只能找到一部分。
If we find number A, we should try to find as much A as we can. In most cases we may find just some of them.
In this example, we can sure most of the 1s, but there are 1 x2 we cannot make sure.
定义5 一刀流 One by One
有一种特殊的标准数独叫做一刀流。如同它的名字，你应当按1~9的顺序去完成它，先做完所有1，接着2，3......最后到9。
There're a special kind classic sudoku for training, they are called 一刀流(One by One). As it's name, you should do it from 1~9, find all 1, all 2, all3...... and all 9 last.
你可以在下面的网址完成它：
You can do it in http://www.sudokufans.org.cn/
这里有两种一刀流，一种可以仅使用宫内隐性唯一完成，另一种需要行列隐性唯一。
There're 2 kinds of 一刀流, one of them can be solved only by only Hidden Singles in Boxes. To solve another one, you must need to search for Hidden Singles in Rows/Columns.
练习 Practice
① 九阶标准数独中，我们如何检查是否找到了所有的5？
In a 9x9 puzzle, how to check have we finished all about number 5?
② 如果需要找到宫内隐性唯一，在4/6/9阶数独中，我们需要多少个已经确定的数字？
If we want to get a Hidden Single in Box, how many known numbers need in 4x4/6x6/9x9 Sudoku?
答案 Answer
① 数一下是不是有9个5。Count if there are 5 x9 in the grid. ② 2/3/4.
