example, if a certain number must occur on a certain line, then occurrences of that number found in a block that intersects this line can be ruled out as candidates. Sometimes called pointing (or matched) pairs (or twins)/triples (triplets) as they point out a candidate that can be removed. Nishio – What-if method of elimination, where the use of a candidate that would make its other (necessary) placements impossible is eliminated. Single (or singleton, or lone number) – The only candidate in a cell. Hidden single – A candidate that appears with others, but only once in a given row, column or box. Locked candidate – A candidate limited to a row or column within a block. Naked pair – Two cells in a row, column or block, which together contain only the same two candidates. These candidates can be excluded from other cells in the same row, column or block. Hidden pair – Two candidates that appear only in two cells in a row, column or block. Other candidates in those two cells can be eliminated. Trio – Three cells in a unit sharing three numbers exclusively. See "Triples and quads". Triples and quads – The concepts applied to pairs can also be applied to triples and quads. X-wing – See N-fish (with N=2). Swordfish – See N-fish (with N=3). N-fish – Analogues of hidden pairs/triples/quads for multiple rows and columns. A pattern formed by all candidate cells for some digit in N rows (or columns), that spans only N columns (rows). All other candidates for that digit in those columns (rows) can then be excluded. Names for various N-fish: 2-fish: X-wing 3-fish: Swordfish 4-fish: Jellyfish 5-fish: Squirmbag – For 9×9 Sudoku, since every N-fish comes paired with a 9-N fish whose effect is the same (thus any 5-fish is paired with a jellyfish; any 6-fish with a swordfish; any 7-fish with an x-wing; any 8-fish with a hidden or naked single). Nevertheless, a 5-fish is occasionally called a squirmbag. 6+ fish: 6-gronk, 7-gronk – these patterns are only useful for Sudoku larger than 9×9. Remote pairs: When a long string of naked pairs that leads around the grid exists, any cells that are in the intersection of the cells at the beginning and the end of the string may not be either of the numbers in the naked pairs, for example, 4 and 7. See also KenKen Sudoku