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.

## Sharing Hanabi’s Secrets

This post details a fireworks analysis on “Hanabi”, shye’s fifth example. The first four examples used matching elbows alone, along with bi-value cells. This one uses forcing chains to identify the value winning placement in the neck cell shared by … Continue reading

## Fireworks 4 Stretches the Matched Elbow Rule.

After a challenging basic, we get two matched pairs on two values again, but this time, linked by a single bv. The second challenge is the application of the matched elbow rule of the last post in a more hypothetical … Continue reading

## Fireworks 3 Matches Elbows and Bv

This post develops a property of a 2 value elbow match, and uses it with matching bv. Before we start on that, here are the elbow panels for the last week’s second example, just in case you want to compare … Continue reading

## X-panel Elbows for Fireworks

This post illustrates the use of the Sysudoku X-panel for fireworks analysis, as introduced  in forum corresponent shye’s first two examples. Here is shye’s statement of the fireworks principle: What does this actually mean? Given a row, column and intersecting … Continue reading

## UHC 397 Fills the Stocking

After two “simple” ANL, Beeby finds a candidate removal by pattern overlay analysis. On PhilsFolly.com, this is requested under “POMs”.  Then a pattern analysis for The Guide offers many more removals using freeforms.   A finned swordfish gets us to coloring, … Continue reading

## An AIC Parade by ultrahardcore 397

This post follows basic with a variety of Alternate Inference Chains. It is an opportunity to compare their effects and corresponding Sysudoku labeling. Three bypass clues, naked triple eliminations, and the line slinks marked in cell corners, that’s the  outcome … Continue reading

## A BARN Storming UHC 353 Finish

This posts finishes left page ultrahardcore 353, using several notable moves to expand a cluster.  Sudokuwiki starts it with a grouped terminal ANL with line and box winks, a regular swordfish expands the cluster, trapping four candidates. Expansion creates an … Continue reading

## Softening left page ultrahardcore 353

Here is another puzzle the DIY oriented solvers suggest is too hard for human solving, even as the moves they find are too instructive to ignore.  This post gets quickly to ALS methods that demand exhaustive enumeration from the DIY … Continue reading

## UHC 309 Rounds the Bases

The ultrahardcore review solvers illustrate a diverse solution path, before and after AIC and cluster building. Here is the grid after the bypass and box marking. Beeby found a naked single SE4 in r8c7 in its basic. The Sysudoku Basic … Continue reading

## The UHC 265 Wrap Up

This post continues on the solution path for left page ultrahardcore 265. We begin where we left off, with the two solvers synchronized and with the first preliminary coloring cluster on the grid. Next, a 3 – ANL creates a … Continue reading