Logic Masters Deutschland e.V.

• Balanced QuattroQuadri: Place the numbers -4 to 4 once each in every 3x3 box such that numbers do not repeat in a row or column.
• Dual Quad/Sum Dots: A number in a circle gives the sum of the four numbers surrounding that circle. Multi-digit sums are written in the balanced nonary numeral system (where the first number is multiplied by 9 and the second number added to it). In addition, each number in that circle must appear at least once in the four cells surrounding that circle.
  • For example, a circle clue with "-1 +3" would have at least one -1 and +3 in its four cells, and also all four numbers (including the indicated -1 and +3) would have to sum to (-1 * 9) + (+3 * 1) = -6.
  • Clarifications: In a two-digit sum, if the higher number is zero, then a zero must appear in the four cells around the clue. If the sum is single-digit, a 0 does not need to appear in those cells (unless the entire sum is 0). If the higher and lower number are the same, then that number must appear at least twice.
• A question mark may represent any number from -4 to 4, but whichever number it represents must obey all the above rules.

• SudokuPad
• Penpa

Solution code: Rows 5 and 6, with a "-" to mark the negative numbers.

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