CHAIN

How to play

Every number is how many steps it is to the nearest well.

A well is a hole, not a number, and it is drawn — some are printed for you and the rest are yours to find. Steps go up, down, left and right, never diagonally. Tap a blank square, then tap a digit or the well key.

• Neighbouring numbers can differ by at most 1.
• Every 1 touches a well; every bigger number touches one exactly one smaller.
• Nothing needs guessing. Every square can be worked out.

What a chain is

The daily is one board, the same for everyone. A chain is the extra: a board that is not published anywhere.

• The code in the address is the board. It is not stored, not listed and not indexed — this page builds the board from the code when you open it.
• Solve it and you are handed the next code. Paste the card wherever you like; whoever opens it gets the same board you were looking at.
• The code is worked out from the printed clues, never from the answer, so a card can never spoil a board.
• Five slips, the same as the daily.

Every chain board is checked before it is drawn: exactly one answer, and reachable by reasoning alone. A board that needed a guess is thrown away and another is built.

Kept on this device. Nothing is sent anywhere and there is nobody to tell.