Marking Gaps with X

Level: Basic

Block off cells that no block can reach with an X to narrow the logic.

Just as important as finding cells to fill is blocking off cells that will stay empty with an X. Mark cells the remaining clues simply cannot reach, and the separating gaps between blocks, with an X.

Once you have confirmed a block, the cells right beside it must often be empty in order to separate it from other blocks. Blocking these with an X makes the positions of neighboring blocks clearer.

X marks do not draw the picture directly, but they act as a lubricant that reduces the possibilities for the remaining cells and leads you into overlap and edge forcing.

Related techniques