Neighbours 9x9 #2 Very Hard (another name is Neighbours, Nachbarn) play free online
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It is a kind of 2d sudoku.
In this variant of the puzzle there are additional conditions:
In adjacent cells, separated by a bold line, there are consecutive numbers. Numbers between which there is no line cannot be consistent. The task is to enter numbers from 1 to 9 into the cells of the cells so that each number meets only once in each horizontal row, in each vertical column.