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Naked pairs: two cells in one unit share the same two candidates; remove them from the other cells of that unit. Works in rows, columns and boxes. Ste...
Naked triples: three cells in a row/column/box share exactly three candidates; eliminate those from the remaining cells. Steps: spot the trio, confirm...
Naked pairs: when two cells in a row/column/box contain the same two candidates, remove those digits from every other cell in that unit. Steps: spot t...
Naked triples: when three cells in a row/column/box hold exactly three candidates between them (e.g., {4,5,6}), eliminate those digits from the rest o...
Hidden pair: two digits occur in exactly two cells of a row/column/box. Clear other candidates from those two cells only; the rest of the unit is unch...
Hidden triple: three digits occur only in three cells of a row/column/box. Remove other candidates from those three cells (not from the rest of the un...
Last remaining cell: if a row/column/box has exactly one valid place for a digit, that digit is fixed there. Steps: spot the nearly complete unit, lis...
Swordfish: if a digit in three rows is confined to the same three columns (or vice versa), remove that digit from the remaining cells of those columns...
Last empty cell: if a box/row/column has only one empty spot, the missing digit goes there. Steps: read present digits, compute the missing one, place...
Last possible number: if exclusions from row, column and box leave a cell with a single candidate, that digit is fixed. Steps: gather candidates, elim...
X-Wing: a digit in two rows appears only in the same two columns (or vice versa). Rectangle formed ⇒ remove that digit from the remaining cells of tho...
Y-Wing: pivot AB with wings AC and BC. The common candidate C is removed from all cells that see both wings. Steps: find pivot+wings, find overlap of ...
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