Double Sweep Lessons From 112 and 133


Two rare double sweeps in the bypass show up this post. In Puzzleproof Extreme 122, it’s a 5-fill line; in 133, a 5-fill box. In each, 5 cells are free and two are claimed by two values, leaving a 3-fill.  Both puzzles are finished in box marking.

How do you prepare to spot this start of basic on Pzlpfx2 112? Two cells to fill in c4 and two values in the South box forced to fill them.

There are many effects from this 4-fill before the list of value effects begins in the bypass.  Is that what happened in your trace?

And how did you represent it in your trace. It’s a 5-fill, but c4[34579]?

I went with a subset pair here, but later added a line to announce the 4-fill in the South box.

If you don’t spot the double sweep 5-fill or the 4-fill, they get resolved later.

 

 

 

 

Here is the grid as the 9: list starts. Here you note the missing 2 and 9 to see both SW48 effects. It’s interesting to follow the collapse from here.

The hidden dublex is easy to spot because the two 9 slinks that create it are added together.

 

 

Instead of the hdx, let’s close with the placement ambiguity that remains just before the decisive NW4, in the “after ellipse” resolution normally omitted. Maybe that lasting ambiguity explains the Puzzleproof claim that this collection is somehow “extreme”.

You think?

 

Moving on to Pzlpfx2 133, the basic trace reveals a crippling bypass, with many unresolved 3-fills.

 

 

 

First is this double sweep N59, leaving Nc5 to fill.  Then the resulting N4 adds the second slink in c6 that joins the one in Ec8 for the hidden dublex Whdx4.

The box marking collapse is straightforward, but if you solve on after the ellipse, you see how long it takes to pin down placements of some values, particularly 3.

Next, the review of Puzzleproof Extreme 2 is completed with 154, 175 and 196.

 

 

 

 

About Sudent

I'm John Welch, a retired engineering professor, father of 3 wonderful daughters and granddad to 7 fabulous grandchildren. Sudoku analysis and illustration is a great hobby and a healthy mental challenge.
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