GridWits
Hard tier Technique 6 of 8 Used by Smart Hint

Saturation Seal

Filling this connection all the way would leave both its islands full, and with them full nothing else could ever leave their group — so it would strand the highlighted islands from the rest of the board. It can't carry that many.

How it works

  1. 1The 2 at the top is already full: its double bridge down to the 4 is all it will ever have, so those two islands are one group and the 2 is no longer a way out of it.
  2. 2The 4 still needs 2 more bridges, and the 2 on its left needs 2 as well.
  3. 3A double bridge between them would fill both at once — every island in the group would then be full, so no bridge could ever leave it again, and the two islands at the bottom would be stranded.
  4. 4So that connection can carry at most a single bridge. Two 1-islands, or two 2-islands facing a double bridge, are the simplest version of this same trap.
2 4 2 2 2
  • Existing bridge
  • Connection capped
  • Islands that establish the pattern
Next in the ladder Cut-Bridge Parity →

This is the only possible connection across a cut: it must be positive, and the clue sum on either side determines whether it is single or double.