Join or Separate Groups

Two small groups of filled cells may have to be joined if they belong to one larger clue.

For example, with the clue 5:

■ ■ · ■ ■

The centre cell must be filled if these cells can only belong to the same block:

■ ■ ■ ■ ■

The opposite situation can also occur. If joining two groups would create a block longer than any available clue, the cell between them must be empty.

For example, if the largest remaining clue is 2:

■ ■ · ■

The unknown cell cannot be filled because that would create four consecutive filled cells:

■ ■ × ■