Normal sudoku rules apply. Shade some cells such that all shaded cells are orthogonally connected, and all unshaded cells are orthogonally connected (a 2x2 area MAY be fully shaded or unshaded). For each N, row N and box N both have exactly N shaded cells, which contain exactly the digits from 1 to N. Adjacent cells on the red line have different parities i.e. one digit is odd and the other digit is even.