Logic Masters Deutschland e.V.

Rules
Divide the grid into four orthogonally connected regions, each containing nine cells.
Fill the grid with the digits 1 to 9, so that no digit repeats in a row, column, or region.
A digit in a circle indicates the number of cells in the same region that are "seen" in all orthogonal directions, including itself. Region borders block sight.
Two circles connected by a line must be in the same region.
In the finished grid, each 2x2 square of cells has to contain at least one low digit (1/2/3), one middle digit (4/5/6), and one high digit (7/8/9) [Global entropy].
Digits along a green line between two circles sum to a two-digit number, where the tens digit is in one circle and the ones digit is in the other.

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