dailysudoku.com

Yes, 17-er quite possible. See "August 14 puzzle grade" thread for an example and see if you can work it through. I don't think it will present much of a problem so long as you don't clutter the board ...

I've answered my own question about whether puzzles with few cells filled in will tend to need trial and error at some point. The following puzzle has only 17 starter cells but can be completed with s ...

On further inspection it works out with just the one "invalid" move (by which I mean an arbitrary trial and error choice from among the candidates that has no logic behind it) not two as I suggested.
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I tried harder and found a solution. It can be reached by two "invalid" moves: r9c3=6 (this allows 47 cells to be completed); then r9c8=1 lets you finish the job.

Not much fun doing them this way th ...

Terry

But you have changed the puzzle. We were given a "7" at r5c7 in the original layout and you have changed that.

Someone-somewhere - do you have a solution as all my attempts to bifurcate have l ...

Looks good, but the puzzle you rated as impossible did not in fact present any special problems -- no hidden triplets, let alone X-wings and whatever. I would have called it something like "Intermedia ...

Dear someone-somewhere

That other thread seems to have been pulled so I'll talk about your formula for predicting candidate scores here. Basically it doesn't work. As I mentioned in an earlier messag ...

Dear someone-smewhere

Obviously I misunderstood what you were offering. What I thought was that you were prepared to use your program to calculate some difficulty indices that people might think up.
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Dear Guest (the one who offered Schwa to run tests on his archive of 200 puzzles)

The offer is mighty generous. Can I take you up on it? I would love to receive a data file with the following numbers ...