Logic Masters Deutschland e.V.

Sum/Difference Lines: Each line connecting two circles is a so-called Sum/Difference Line. One of the circled values indicates the sum of all digits along the line.
The other circled value indicates the difference between the highest and the lowest value on the line. (Which circle indicates the sum and which the difference has to be determined by the solver.
If a circle is bounding multiple lines, it may serve different purposes for those, i.e. it can indicate the sum for one line and the maximal difference of another one.)
Copycat Cells: Place 9 Copycat Cells into the grid so that there is exactly one Copycat Cell in each row, column, and 3x3 box.
Each Copycat Cell must contain a different digit.
The value of a Copycat Cell is the digit in the cell rotationally opposite itself in the grid (180° rotation about the center of the grid). For example, if r2c3 is a Copycat Cell containing the digit 5, and r8c7 contains the digit 9, the value of r2c3 is the digit in r8c7, which is 9.
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