1, exclusion method (exclusion method)

Exclusion method: using numbers to find the only space that can be filled in a cell is called exclusion method, and the only space that can be filled with numbers is called hidden list.

According to the different scope of action, elimination schemes can be divided into the following three types:

The only space that can be filled in a number is called hidden single in box in the unit of "palace", which is also called palace exclusion method.

The only space that a number can fill is called hidden single line in the "row" cell, which is also called row exclusion method.

The only space that a number can fill is called the hidden single column in the "row" cell, also known as the row exclusion method.

2. Unique residual method

Unique remainder method: finding the unique fillable number with lattice is called remainder method, and finding the unique fillable number with lattice is called naked list.

The remainder method is a method to delete the numbers that have appeared in peer groups, and each peer group has 20 peer groups, as shown in Figure 7.

Second, the block exclusion method

Block exclusion method includes palace block pointing method and column block claim method.

In basic problems, the block elimination method can replace the observation of some basic solutions or assist the basic solutions to find the focus. In non-basic problems, building blocks can hide any other structures, simple ones can hide basic solutions, and difficult ones can hide hidden numbers pairs and other advanced skills.