What is kropki sudoku...

Final one for the moment that I'm going to look at - called kropki sudoku.

This is a fun variant of sudoku where one sees the usual sudoku grid, but also sees lots of little white dots or black dots.

These white and black dots are placed on the lines between two different cells.

So you can probably guess that the dots indicate some sort of relationship between the cells, and that relationship is different depending on whether or not the dot is a white one or a black one.

So what is the rule that is indicted by the black and white dots in kropki sudoku?

Well they indicate pairs of numbers that are either consecutive (like 2 and 3) or one is the double of the other (like 2 and 4, 3 and 6 etc).

There are two version of the puzzle - one where *every* such relationship is marked in where it occurs in the grid, and a second where only some are marked in. Clearly it is very important to know which version of the rules the particular kropki puzzle you do use, as otherwise you will go horribly wrong, or just not be able to solve it!