Place the digits 0-9, once each, into every row, column and 3x3 box. To enable this, one cell in every row, column and 3x3 box is a “Schrödinger cell” that contains two digits. This cell counts as the sum of its digits for the purposes of the zipper line rule below. Digits an equal distance from the circled centre of a lavender zipper line sum to the same number. The grid is partially covered in fog. Placing correct digits reveals clues in the surrounding 3x3 area. For the avoidance of doubt, if two strands of the same zipper line enter a single cell then the digit in that cell must be counted twice in determining its contribution to the line.