A General Logic for Sudoku

A Strong Finned Fish?


Points. Set triplets are relatively rare in simple logic but do occur. Set triplets can raise the rank of logic except along its minor branch. 



Set Triplet Defines Rank 0 Region




The logic in this example is almost a swordfish except it is missing one candidate. The logic is completed by box 5, which makes a strong link from 1r6c6 to 1r4c5 where it forms set triplet A. By set theory rules, the logic has 4 sets, 4 linksets and a basic rank of 0. However, the set-triplet raises the effective rank to 1 everywhere except along its minor (linkset) branch, which is still rank 0. The branch includes linksets r21 and r41, which are both rank 0 as indicated by the black highlight (below). This eliminates candidate 1r4c8.