Done. 1 bad guess.

Done, crosshatching only

done

ng/ng - just a little endgame uniqueness constraint

done

dang, quickest I've ever done an expert, felt more like an easy or at worst a medium

g0

Two guesses

Difficulty score 40. No green.

Wow, this seems simple....

I guess I am an expert....maybe?

No "expert" techniques were disturbed in the solving of this puzzle

Limer, the "expert" designation doesn't mean a lot by itself. Though lord knows *I* typically can't do them without greens.

Though it's flawed as well, drwho's rating system seems to be a better marker for what's difficult.

Did it, no green, no guess. It had an "either way, mark it down," two alternate inputs yielded the same output.

I just finished the back catalogue, and I'm all caught up for the first time ever.

When do the money and fame start rolling in? I've put my phone on vibrate so the constant calls from the press won't annoy me too much.

So. What now?

start

ding

I'm caught up to SJ

go

done

Thanks to drwho for putting a name to the technique of alternating inference chains (AIC) in his April 23 comments. I have been using the technique for a while as a way to speed through experts without doing anything that could be called guessing. However, my experiences have now started me wondering whether there is any real difference between the following two general approaches:

Approach 1: Figure out what will be the consequences if a cell contains (or does not contain) a particular number, as in AIC, and then enter (or delete) numbers only when those actions have been proved to be correct.

Approach 2: Save a checkpoint, then enter (or delete) that particular number from that cell, and discover whether the consequences lead to a solution, to nishio, or to uncertainty. If no solution is reached, return to the checkpoint and make a different choice.

It seems to me that the second approach is just as structured as the first, and the main difference is that the first method looks for small, logical steps towards a solution while the second method says I don't need to solve the puzzle by small increments, I only need to find the solution by an overall logical method. And so, when I see comments such as "I needed three guesses," I can't help wondering whether someone else might say, "I patiently eliminated two impossibilities on my journey to the solution."

As a relative newcomer to Sudoku, I expect that other players have sorted out this issue long ago. Would someone care to enlighten me?