A General Logic for Sudoku

ALS Backbone for 3D Kraken Like Fish

Points. ALS and similar structures are often found embedded in set logic eliminations.

ALS Backbone for 3D Kraken Like Fish

This elimination was the first difficult move in solving Top1465 #77. The structure is made mostly from two ALS, the first formed by 3 cell sets in box 1, and the second by 3 column sets in column 5 (columns 3 and 9 overlay each other in the 2D diagram). It has no triplets. The logic is rank 1 and the elimination of 6r2c6 is caused by the overlap of row set r26 and cell set c66, highlighted red and green respectively.