16 char Sudoku
Definition
Circled numbers, two couples of numbers in the same row, above and below, and to the left and right of the same person (column) in both upper and lower (left and right) palaces (a cross or T-shaped structure, a total of five nine palaces). There are three couples in total, and three pairs of people in the same row.
If you remove the two-lined numbers, the other two numbers above and below the column with the same palace, called couple numbers, exist in both the upper and lower two palaces, making three couples.
Underlined numbers, the other two numbers to the left and right of the row with the same palace, called couple numbers, exist in both the upper and lower two palaces with couple numbers, making three couples.
Normal numbers, numbers that do not have additional marks and do not belong to the descriptions defined in 1, 2, and 3. Belongs to the "couple numbers".
(See "Sudoku Holes")