Logic Masters Deutschland e.V.

The shading of this (Little) Killer Sudoku gives rise to a subordinate puzzle of Neighbours, where the cell values have to be taken modulo 3. (Complete list of rules below.) This is a follow-up of Residual Neighbours Sudoku I. 1. Normal sudoku rules apply, i.e., every row, column and indicated 3-by-3-box contains the digits 1-9 once each;
2. normal Little Killer rules apply, i.e., the clues outside the grid the give the sum of the digits along the indicated diagonals;
3. normal Killer rules apply, i.e., digits cannot repeat within a cage (no cage totals are given);
4. in addition, the residue classes of the digits modulo 3 constitute a grid of neighbours, i.e., a cell is shaded in grey if and only if it is not congruent modulo 3 to any of its orthogonal neighbours; e.g., if a cell is shaded and contains a 5, then none of the orthogonally adjacent cells can contain a 2 or an 8 and conversely, if it is unshaded, (at least) one of the adjacent cells must contain a 2 or an 8.

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