Logic Masters Deutschland e.V.

Author: 真笑(洪卫华), from China, this question comes from his personal blog.

This is a new variant of Sandwich Sudoku. It is created using the variable order of the sandwich numbers. It is also the fourth question of the series. There may be more interesting combinations of variants later.

69Sandwich(4)-Uncertain Double Sandwich
1. Classic Sudoku rules apply;
2. If X appears in front of Y, the sum of all the numbers between X and Y is marked on the outside (left or upper black);
3. If M appears in front of N,the sum of all the numbers between M and N is marked on the outside (left or upper gray);
4. XYMN is 4 different numbers, where the difference between the number X and the number Y is 1, and the difference between the number M and the number N is 1.
5.All qualified outside prompt numbers have been marked.

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