Normal Sudoku rules apply. Diagonals must contain the digits 1-9 exactly once. The inequality sign points to the lower of the two cells it connects. The black dot indicates that one of the connected cells must be double the other. The "taxicab" distance between two cells is the minimum number of orthogonal moves required to go from cell A to cell B. In the completed grid, ONLY the red cells contain digits that are their taxicab distance away from another cell containing the same digit. For example, if cell A and B both contain 8 and had a taxicab distance of 8 between them then they MUST both be red. No two white cells have this property. Of the set of digits 1 to 9, only a subset (whose sum is less than 15) can appear in the red squares.