Train
Technique Practice
Pick a technique and work through three stages. Every puzzle is generated so that the technique actually appears in the logical solve path.
Guided
Unlimited hints, mistakes do not end the run.
Drill
One hint per puzzle, three mistakes allowed.
Challenge
No hints at all, three mistakes allowed.
Advanced
- Advanced
AIC
Alternating Inference Chains eliminate candidates through strong and weak links.
Guide only — no drill for this technique
- Advanced
Swordfish
Three rows and three columns align for one digit — like an X-Wing with an extra line.
Guided–Drill0/3Challenge–0/3 stages - Advanced
X-Wing
A digit forms a rectangle across two rows and two columns.
Guided–Drill0/3Challenge–0/3 stages - Advanced
XY-Wing
A pivot cell with two candidates links two wings to eliminate a shared digit.
Guided–Drill0/3Challenge–0/3 stages
Intermediate
- Intermediate
Hidden Quad
Four digits can only appear in four cells of a unit.
Guided–Drill0/3Challenge–0/3 stages - Intermediate
Naked Quad
Four cells in a unit share exactly four candidates between them.
Guided–Drill0/3Challenge–0/3 stages - Intermediate
Hidden Triple
Three digits are confined to three cells in a unit.
Guided–Drill0/3Challenge–0/3 stages - Intermediate
Naked Triple
Three cells collectively contain exactly three candidates.
Guided–Drill0/3Challenge–0/3 stages - Intermediate
Box/Line Reduction
A digit in a row or column is confined to a single box.
Guided–Drill0/3Challenge–0/3 stages - Intermediate
Pointing Pair
All candidates for a digit in a box lie on one row or column.
Guided–Drill0/3Challenge–0/3 stages - Intermediate
Hidden Pair
Two digits can only appear in the same two cells of a unit.
Guided–Drill0/3Challenge–0/3 stages - Intermediate
Naked Pair
Two cells share exactly the same two candidates.
Guided–Drill0/3Challenge–0/3 stages