Fill in the grids so that every row, every column and 3x3 box contains the digits 1 through 9. There must be a one-to-one correspondence between both twins, i. e., in all positions with a certain digit in the first grid must be in the corresponding position in the second grid also always the same digit (possibly another as in the first grid).

Fill in the grids so that every row, every column and 3x3 box contains the digits 1 through 9. The sum of the digits within each sub-region is equal to the specified number. There must be a one-to-one correspondence between both twins, i. e., in all positions with a certain digit in the first grid must be in the corresponding position in the second grid also always the same digit (possibly another as in the first grid).

Fill in the grids so that every row, every column and 3x3 box contains the digits 1 through 9. There must be a one-to-one correspondence between both twins, i. e., in all positions with a certain digit in the first grid must be in the corresponding position in the second grid also always the same digit (possibly another as in the first grid). Numbers going along grey lines must be in increasing or decreasing order from one end to the other.

Fill each 4x4 grid with the digits 1 to 4 so that each row and column of each 4x4 grid has each digit. Neighboring squares from separate grids do not have the same number.

Fill the grid with the digits 1 to 9. Each row, column and 3x3-box has exactly one of each digit. The four edges of the green square must contain the same set of digits (possibly in different orders). None edge of this square contains a repeated digit.

Fill in the grid so that every row, every column and the 3x3 boxes contain the digits 1 through 9. In the yellow cells there are 7 different values.

Fill in the grid so that every row, every column and the 3x3 boxes contain the digits 1 through 9. In the yellow cells there are 7 different values.

Fill in the grid so that every row, every column and the 3x3 boxes contain the digits 1 through 9. In the yellow cells there are 7 different values.

Fill in the grid so that every row, every column and the 3x3 boxes contain the digits 1 through 9. In the yellow cells there are 6 different values.