Kropki Sudoku

Rules

Fill the grid so that every row, every column and every 3x3 box contains the digits from 1 to 9 exactly once. A white dot between two adjacent cells requires that the value in one cell is exactly 1 greater than the value of the other cell (e.g. 3 & 4). A black dot between two adjacent cells requires that the value in one cell is exactly double the value of the other cell (e.g. 3 & 6). If there is no dot between two cells then none of the two conditions must be fulfilled.