Sorry about last week’s post arriving a week earlly. This week continues the solving of Stefan Heine’s ultrahardcore 311 with a coloring trial, and an enabled Beeby marching to the solution.
Here is the trial grid, after the removal of the toxic orphan last week.
With orange on trial, blue is confirmed quickly,
the hidden UR removes 2r9c2, and W6 removes the last 5 candidate in the West box, placing the red army,
, but leaving the blue green cluster unresolved,
The naked quad in r8 leaves SE1 and an expanded cluster trapping 4r6c7, and bringing
a naked triple in c6, and
another hidden unique rectangle, followed by
an ALS_85, with a SWc1 boxline removal.
Beeby now recycles the ALS to use its internal slink between two single value groups as the starting slink in a 1-way. 1r9c6 is made false directly if 1r7c6 is true, and by the AIC if it is false.
After (S1, S5) and the 9r7c1 expansion trap, Beeby launches another 1-way from a line slink, this time, 2r4c6. If the starter is false the chain removes the victim straight up.
Beeby lines up two ALS against the combinations of two cells in this APE. There’s no APE button but this is a Beeby ALS “other”.
After the follow up
traps 6r4c3,
blue is wrapped as 8r6c4 turns blue, and the grid turns green..
Next week, its Stefan Heine’s ultrahardcore 355.
Systematic Sudoku 