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,
followed by a grouped confirming ANL barely aided by the cluster.
After the follow up
a regular swordfish
expands the cluster, trapping four candidates.
Expansion creates an XY ANL, that you can also label as a 451-wing, or as a 3-BARN.
Sudokuwiki finds a 4-BARN, a Bent Almost Restricted 4-set. Of the 4 values 1589 confined within the bent region Wc1, 3 are restricted within units, 1 in W and 8,9 in c1. The set is “almost restricted” because Wc1 value 5 is not restricted to a box or a line. An outside candidate 5r9c2 sees both candidates of the unrestricted value. The Guide explains the logic.
Now the cluster expands to trap 5 and claim NW7 and SW2,
and a shortcut XY chain wraps green.
An easy wrap, but so hard to get here.
Next is left side ultrahardcore 397.
Want to make it the last one, or do we add two more?
Systematic Sudoku 