## Rules

Doppelblock rules : shade exactly two cells in each row and each column. In the remaining cells, place an integer between 1 and X-2, where X is the number of cells in each row, such that each number appears exactly once in each row and each column. Number outside the grid indicate the sum of the numbers between the two shaded cells. Some cells may already be filled for you.

## Example

Here is an example of a Doppelblock grid and its solution

Solve online here

## History of Doppelblock

According to the WPC unofficial wiki, doppelblock appeared in online qualifier for the Japan Puzzle Championship 2016 by an unknown author. It was latter independently created by Naoki Inaba (Japan).