Guidebook
Advanced Sudoku Techniques
When singles stall, lean on structure: locked candidates, fish patterns, chains, and coloring to keep progress calm and logical.
Elimination
Pointing Pairs / Triples
Lock candidates within a box to clear rows/columns and open new singles.
Elimination
Box–Line Reduction
Use line-locked candidates to thin boxes and reveal follow-up singles.
Pattern
X-Wing
Spot two-line fish to wipe out candidate clutter before resorting to chains.
Pattern
Swordfish
Scale the X-Wing idea to three lines for tougher grids that resist basics.
Pattern
Jellyfish
Four-line fish for extreme cases—use sparingly when other patterns fail.
Chains
XY-Wing
Pivot on a hinge cell to eliminate a shared candidate across two wings.
Chains
XYZ-Wing
Add a third candidate to force a single elimination from the hinge cell.
Chains
W-Wing
Pair two bivalue cells with the same digits and a linking conjugate pair.
Chains
AICs & Forcing Chains
Alternate strong/weak links to drive eliminations without guessing.
Logic
Coloring & Multi-Coloring
Track conjugate pairs with colors to prove contradictions and force placements.
Uniqueness
Unique Rectangles
Prevent deadly patterns by eliminating candidates that would create multiple solutions.
Variants
Finned & Sashimi Fish
Handle imperfect fish shapes by checking fin positions for targeted clears.
ALS
Almost Locked Sets
Use near-complete sets to create strong/weak links and chain into eliminations.
Hybrid
Sue de Coq
Combine row, column, and box logic to lock down complex candidate groups.