Normally I try to keep constraints to a single grid, while populating overlapping boxes with competing constraints. The idea of a single line meandering over all four grids wouldn’t leave me alone, and I’m glad. I like this puzzle, and was still able to keep white dots in the black grid, black dots in the red grid, XV clues in the green grid, and quads in the blue grid.
This puzzle might be easier to work with in SudokuPad if you click settings, choose “Experimental”, scroll down, and set “Test Large Puzzle UI” to “On.”
I have room for even more editorial content. But I’ve just finished writing content for the previous twelve puzzles back-to-back, so I’m feeling creatively bereft–as evidenced by the text introducing the previous twelve puzzles.
Rules:
Normal Gattai-4 rules apply. That is, there are four overlapping 9x9 Sudoku grids. Within each Sudoku grid, each row, column, and 3x3 box contains the digits 1-9. Overlapping boxes are shared by the overlapping grids.
Cells separated by a white dot contain consecutive digits.
In cells separated by a black dot, one digit is double the other.
Digits in cells separated by an X sum to 10. Digits in cells separated by a V sum to 5.
Digits within circles appear at least once in cells touching the circle.
There is a single Region Sum Line shared by all four grids. Thick region borders divide the line into segments on which the digits have the same sum.
Estimated difficulty: 1.5 out of 5
Solve on SudokuPad