The Bypass 3-Fill Smacks Diabolical 350

This post starts with a trace of the merciless 3-fill pounding of Ardson’s Sudoku Diabolical 350 in the bypass. Highlight grids from adv2 110 and 190 then follow.

The 3-fill brings on the unit fill phase of basic solving, when fills take precedence over number order, much sooner. The challenge is to avoid overlooking 3-fill opportunities. Writing out the 3-fill strings in the trace is effective for me, but you may find that I have overlooked a few.

 After the effects of NW1 are explored, the main list resumes with N3.

 Here is the grid near the end of the first leg, after C3. Single pencil marks indicate effects not yet explored as causes.







Diabolical 110 offers another kind of highlight, a near-BUG right out of the bypass. Filling in the 3-fills where possible, and coloring, you get traps and a blue wrap in the SE box, and a green solution.




In case you’d like to watch this happen, here’s the basic trace.




Sudoku Diabolical 190 is also reduced to a bv sandbox by the 3-fill. After these bypass actions,

and easy box and line marking, 190 is vulnerable to the two bv predators, XY chains and coloring clusters.

First, two XY- chains make three removals. One is removed by boxline as well.








Then coloring is decisive as two blue candidates are forced in r4c2.

Next week, a full backup of your solution on Sudoku Diabolical 310. In this review, it’s saving the best for last.

Be kind to your Valentine.

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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