This post calls on pattern directed coloring trials to solve IV-24, a puzzle in Rebecca Bean’s Extremely Hard, vol. 10. This one that seems to defy almost all advanced methods, and therefore, to deserve the rank of “extreme”. This also makes IV-24 a good candidate for refining or expanding the Sysudoku Advanced repertoire as the Sysudoku Guide is put together in the pages. In Bean’s rating system, however, it stands 7th.
More accommodating to the bypass than most v. 10‘s, VI-24 clams up beyond that in basic.
Basic arrives in the grid below, which is destined to be a test plot for refining methods prior to coloring.
The reason for that is, I found only this indecisive X-chain ANL before attempting to classify the bv into coloring networks.
There seems to be four clusters with some bridging implications:
not(red and tan) => orange or aqua
not(green and lavender) => blue or yellow
not(lavender and tan) => yellow or aqua
No bridge eliminations come up. That would be a candidate seeing both orange and aqua, blue and yellow, or yellow and aqua.
We do notice two colors appearing twice in the color conflicts above, tan and lavender. If we put tan on trial, orange and yellow take sides with tan. If we try lavender, blue and aqua will jump in.
We go with tan, because it looks less scattered.
Yellow and orange rat on tan, confining S 2’s to r8, and placing SE2 in r8.
I needed a trial trace here.
Unanticipated but welcome, aqua brings in blue on the cleanup crew. We call upon a freeform diagram drawn earlier for a possible toe hold. Blue has three possible patterns for 4, one through yellow and two through lavender.
We choose the more decisive, yellow. In a trial, we want a quick contradiction, leading to a immediate confession. Call it the Perry Mason strategy.
It’s not so quick, but yellow fails, bringing in red, but placing two 9’s in c4. This leaves two 4-patterns for lavender to resolve.
Lavender brings in orange, and it takes both to place NE4 to reject the dotted pattern.
Whew! Extremely Hard.
Next week, the Rebecca Bean Extremely Hard v.10 review is completed with highlights from the last three review puzzles.
Systematic Sudoku 