An easy basic workout, with help from 3-fills, a hidden single, many naked pairs, and a hidden dublex in Beware 135, the fourth in the review of Will Shortz’ Hard Sudoku, v.1. And two suggestions for Sysudoku readers.
The basic trace shows a collapse in early line marking.
Immediate effects are indented under causes.
3-forms are signaled first by the unit names and square bracketed lists of values.
Line pairs and other line subsets are denoted by ‘s’ and a list of values.
The grid after the bypass shows the fill strings for claimed chutes. Row 6 has one string for the chute and one for the remaining 3-fill.
Chutes are marked in box marking. Corner and side placement of pencil marks signals strong links (slinks) and aligned (chute) triples. Box slinks on top corners, row slinks bottom left, column slinks bottom right. Middle bottom marks for row chutes and middle right side for column chutes.
So far this isn’t done elsewhere. Most Sudoku experts aren’t into human engineering as yet. Encourage them.
Here is the line marked grid, at the hidden single 9 in the East box. Bi-value cells (bv) are outlined in green. Candidates in marked lines that are not slink partners are in a list starting on the middle left side of the cell.
We don’t add these candidates to the grid until they are needed. The fill string process is simple and efficient.
That’s more human engineering rarely suggested elsewhere. Proven since 2011. Tell your favorite Sudoku guru it’s about time.
Next is Beware! Very Challenging 145. Like the other 9 in the Hard Sudoku, v1. review, it will not spoil your weekend.
For its examples in support of the Guide’s pattern analysis, the Krazy Dad’s Insane collection will be the first past review to be updated to current Sysudoku conventions. This collection is among the hardest I have reviewed, and a favorite.