Divide the grid into nine regions, each consisting of nine orthogonally-connected cells. Each row, column and region must contain the digits 1 to 9, once each. Zipper lines: Digits an equal distance from the centre of the purple line must sum to the digit in the centre of that purple line. Different zippers don't share cells with each other. The digit in the centre of a purple line counts how many regions contain at least one cell on that purple line. Some region borders are given. Entering a correct digit clears fog in its cell, and may or may not clear fog in other cells. No guessing is necessary.