A General Logic for Sudoku

Siamese Loops, Hit from Both Sides


Points. Double and multiple loops can be connected many ways producing rank 0, rank 1, or rank 2 logic. However, eliminations are determined only by the basic rank rules.



Siamese  Loops, Hit from Both Sides




This piece of logic would have been two independent continuous nice loops, one with row and column sets on the left, and the other with box and cell sets on the right. However, they are joined by a single linkset in row 5, linkset r52, which makes the entire structure a uniform rank 1. The unfortunate candidate sits at the crossing point of two linksets, one from each loop, which causes its elimination.