## CLEF Homework on Unsolvable 190

Here is a checkpoint Sysudoku reader’s homework on the Sysudoku Cross Line Exocet Filter introduced in the previous post.

Was it hard?  I stumbled many times on the 3467 case of the last week, and I may need corrections on this homework checkpoint.  If you sailed through it, you may be close to doing it mentally.

First, the 3&7, 4&6 table. From the grid, blue base digits 3 and 7 force 4 in green target 2. Both 3,7 placements are viable with those green targets.

We can do a single trial with 3 and 7 in either target, and the green target clues.  The trial stalls with the targets unresolved.  The earlier encountered  remote pair and the 125-wing push it a little further.

Then we try 3 in blue target  1, arriving at the inconsistent coloring seen earlier in the orange 8-pattern trial. On 190, the pattern trials were just as decisive as the exocet solution trials.  Then 7 in blue target 1 goes all the way to the solution.

You would have little reason to follow up after getting to the solution, but if you want to check me out on the remaining trial reductions:

The 4&6 with 3&7 trial would start with a naked pair 46 in the blue targets, 3 in green 1 and 7 in green2.

Two of four target arrangements are accepted for the 4&7, 3&6 trials. A single trial with  naked pair 47 in blue and t1=3, t2=6 in green, might suffice.

Finally, for 6&7 with 3 & 4, the grid requires 4 in green target 4. A single trial with 67 in the blue targets,  and 3 and 4 clues in the green.

To recap the two posts, CLEF is demonstrated here as a systematic procedure to make exocet trials in puzzles like Unsolvable 190 more humanly practical. Finally, we can let Unsolvable 190 RIP, with our thanks to Andrew Stuart.

Next, we catch our breath with Charlie Jacobs’s Sudoku for the Brave, a very tough, but basic solving collection.  Down the road, more Unsolvables.  Among them  a direct comparison of CLEF with Bird’s compendium technique.  And if you want to get there first, to CLEF the first monster of my blog, the Golden Nugget.  I knew that would get your attention.