The rule of One is Done

If you've stumbled across this blog (and believe me, I can see the stats -- I know how unlikely that is!) it's either because I've linked to something you posted, or because you are very interested in sudoku, and probably also very good at it.  You probably use scanning or slice and dice, or whatever you're calling it these days very easily, or you're used to counting away all the possibilities in a space to find the one remaining possibility.  You know how to find "twins" and "triplets", even hidden ones.

But just in case, there's an excellent visual tutorial of the sudoku moves done by Conceptis over here.

You can watch the youtube version below, but if you follow the link you can stop and look at each move separately.

It's pretty cool, actually.

But it does kind of take the slow route to some of the answers.  We can do better than that.  Tomorrow (hopefully) I'll explain why keeping set logic in your head (as well as space logic and symbol logic) will give you an edge on the hardest problems.

And I'll answer the challenge, too.