This post completes a coloring solution of Stefan Heine’s left page ultrahardcore 89. Two examples of cluster exit AIC building bring a second finned swordfish, and a cluster exit wrap of the large cluster.
After this follow up of last week’s finned swordfish,
Beeby finds a 7 link XY chain through the cluster to 1r3c4. Beeby doesn’t stoop to Medusa coloring, but we do. Think of it this way. Build an AIC out of a large cluster to an outside candidate. Now any cluster candidate of the same value, and color opposite the exit color is a possible ANL partner, and there is a cluster AIC to it. Just draw in the corresponding strong link.
As a cluster exit from orange 1r3c4, this XY ANL removing 6r3c5 suggests we also look for another red 6 ANL terminal. One red 6 claims two victims, one claimed by the second. When we play the other end as an exit from red 9r5c4, we’re looking for an orange 6 ANL partner for 6r4c5.
The r3c7 removal allows a short XY ANL with green terminals, wrapping blue.
The red/orange expansion
lines up another finned swordfish, we didn’t really need, because
an easy cluster exit wraps orange.
Next time, Stephan Heine’s left page ultrahardcore 89 + 44 = 133.
Systematic Sudoku 