Tapa: one wall, no 2×2
The wall is one piece with no solid 2×2 blocks. Those two rules settle cells the clues can’t reach, and they rule out fits that would break them.
How it works
The shaded cells form one wall: every wall cell joins the others side to side, and no 2×2 square is all wall.
No 2×2: when three cells of a square are wall, the fourth is white.
One piece: a piece of wall with only one open side must grow through it. A cell that white cells cut off from all the wall can’t be wall. And a cell the pieces must pass through to meet is wall.
Room to grow: some ways to fit a clue would trap a piece of wall in white cells or fill a 2×2. Rule those out, then see what the other fits agree on.
Look at the wall, not just the clues
After a few clue fits, the board fills with short pieces of wall. Ask of each one: where can it still grow? A piece with one open side has no choice.
Late in a puzzle, white cells box in areas of the grid. A cell inside such an area can’t be wall, because the wall would be in two pieces.
Worth memorizing
Three wall cells in a square: the fourth is white.
One open side means grow there.
The wall is one piece.
A fit that traps wall is ruled out.
So is one that fills a 2×2.
Practice
0 of 4 rightWhat is the ringed cell?
What is the ringed cell?
What is the ringed cell?
Using clue fit, no 2×2 and one wall, then room to grow: what is the ringed cell?