## Funster Extreme 4 has a Near BUG

The review of the Extreme section of Charles Timmerman’s Funster Hard to Extreme Sudoku is underway, with Funster Extreme 4. Funx 4 has a near BUG, but it gets to the doctor early and takes Dr. Stuart’s medicine dutifully. An extreme crisis is avoided.

This book has 134 Hard, 134 Very Hard, and 134 Extreme puzzles. For this review, I’ve preselected Extremes 4, 18, 32, . . . , 130. We’ll see them through the sysudokie process, allowing for comparison with the 28 earlier collection reviews. You’ll get to try them first, then compare results with mine. I show every step with traces and analysis, but you’re under no such obligation.

Before we begin to checkpoint your efforts on Funster Extreme 4 (funx 4 for short), let’s stipulate a friendly, but fundamental difference of opinion Sysudoku has with author Charles Timmerman. Under the jacket claim that the book is “Carefully designed for advanced Sudoku solvers” there is this quality claim:

Whoa! This claim ignores the human “solving analysis” that will now go to eliminating candidates that sysudokies never put in. It also overlooks the fact that the basic eliminations that have to be made could have been performed on a simpler, much less distracting grid. No one familiar with the challenges of the bypass and the critical role of strong links in advanced solving analysis would describe Sysudoku basic as “tedious”.

That said, if you just transfer the givens to a clean puzzle template like I do, the extreme section of this book is easier.

Here is the Funx 4 grid after Sysudoku basic. Count the added clues, the bv, the box slinks and the line slinks. Are they clearly marked? Now if you have the keypad grid of Timmerman basic, compare grids.

This one begs for XY chains and coloring.

Did your grid go less far or farther? Then read the trace and find out exactly why.

In my case, the 9 candidates were all connected by slinks. Adding a blue/green cluster to see how far it would go, I saw the black XY chain connected two of them. Nothing new there, but the red extension to connect blue 9 with blue 9 confirms blue,  wrapping green.

The  blue to blue ANL slink shows at least one terminal is true, so all blue are true.

The follow-up brings a near BUG, almost a Bi-value Universal Grave. Only one cell holds three candidates. A second cluster demonstrates this, and wraps orange with two orange 1’s asserted in r7 and c1. Andrew Stuart’s Logic of Sudoku rule, to place the twice repeated candidate in the 3 – candidate cell, also works here, eliminating all orange candidates.

Sometimes, being this close to a multiple solution makes a puzzle very difficult. But no puzzle this easily managed by coloring should be considered extreme.

Next is funster Extreme 18, another opportunity to compare working with “printed candidate numbers” and DIY with Sysudoku Basic.

Also, for  Guide readers, the page on XY ANL and remote pairs is up.