Techniques

Each guide explains one technique in plain words. Cells are written rXcY: row X, column Y. The in-app hint tells you which technique it used, so you can come here to read about it.

01 Singles

EasyFull HouseA row, column or box with only one empty cell left. EasyNaked SingleA cell with only one candidate left. EasyHidden SingleA digit that fits in only one cell of a row, column or box.

02 Intersections

EasyLocked CandidatesA digit confined to the overlap of a box and a line (also called pointing pairs, claiming).

03 Subsets

MediumNaked Pair, Triple and QuadN cells in a unit that together hold only N digits. MediumHidden Pair, Triple and QuadN digits that can only go into the same N cells of a unit.

04 Basic Fish

HardX-WingA digit in two rows that is limited to the same two columns. HardSwordfish and JellyfishThe X-Wing idea with three (or four) rows and columns.

05 Single Digit Patterns

HardSkyscraperTwo rows (or columns) where a digit has two candidates each and they line up on one side. Hard2-String KiteA row strong link and a column strong link joined inside one box. HardEmpty RectangleA box where a digit lies only in one row and one column, forming a cross, combined with a strong link. HardTurbot FishStrong link, weak link, strong link on one digit; the two ends cannot both be false.

06 Uniqueness

HardUniqueness techniquesAvoid patterns that would give a puzzle two solutions. HardHidden and Avoidable Rectangles, BUG+1More uniqueness techniques: the puzzle has only one solution, so some patterns cannot occur.

07 Wings

HardXY-WingA pivot with candidates {X,Y} and two pincers {X,Z} and {Y,Z}. HardXYZ-WingLike an XY-Wing but the pivot has three candidates {X,Y,Z}. HardW-WingTwo identical bi-value cells joined by a strong link on one of their digits.

08 Coloring

HardSimple ColorsColor a chain of strong links for one digit with two alternating colors. HardMulti ColorsSimple Colors with two or more separate chains for the same digit.

09 Chains and Loops

HardXY-Chain and Remote PairsA chain of bi-value cells where each shares one digit with the next. UnfairX-ChainA longer Turbot Fish: strong and weak links alternate, all on one digit. UnfairNice Loops and AICsAlternating inference chains that mix strong and weak links. ExtremeForcing Chains and NetsFollow the consequences of a candidate being true or false until they agree.

10 Almost Locked Sets

UnfairALS-XZTwo almost locked sets linked by a restricted common digit. UnfairALS-XY-WingThree almost locked sets: C is linked to A and to B by two different restricted commons. UnfairALS-ChainA chain of almost locked sets linked by restricted commons. UnfairDeath BlossomA cell whose every candidate has its own almost locked set.

11 Finned & Complex Fish

HardFinned and Sashimi FishA fish with one or two extra candidates (fins) next to a corner. UnfairFranken and Mutant FishFish whose base or cover sets include boxes (Franken) or mix rows, columns and boxes (Mutant). ExtremeKraken FishA finned fish where chains, not the fin geometry, prove the elimination.

12 Miscellaneous

UnfairSue de CoqThe cells where a box meets a line, plus one set of cells in the line and one in the box, form a locked set.

13 Last Resort

ExtremeTemplates (for computers)All ways to place one digit in the whole grid, checked against what is known.