Locked Candidates Type 1 (Pointing)

Also called Pointing Pair, Pointing Triple, Box-Line Interaction, Type 1 Locked Candidates.

New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.

What it means

Inside one box, every spot left for a digit sits in the same row or column. The box has to use that digit somewhere, so it lands on that line. Rub the digit out of the rest of the line.

The exact rule, for stronger players

The rule, stated exactly: For a box B and digit d, if every candidate of d within B lies in a single line L (row or column), then d may be eliminated from the cells of L outside B.

What it removes: Remove d from all cells of L that are not in B.

Why it works: d must appear somewhere in B. Every available position is on L, so d occupies a cell of L. Since d appears once per line, no other cell of L can hold it.

Worked examples

These come from real Proven Sudoku boards. Nobody drew them by hand to make the pattern look neat. Each one is checked first, so the board is one you could really meet, the pattern is really there, and every digit it rules out is really wrong.

Sudoku grid showing Locked Candidates Type 1 (Pointing). Every 2 in b4 lies in r4, so the 2 for that box is somewhere on that line and can be removed from the rest of it. — Every 2 in b4 lies in r4, so the 2 for that box is somewhere on that line and can be removed from the rest of it.

Sudoku grid showing Locked Candidates Type 1 (Pointing). Every 1 in b3 lies in c9, so the 1 for that box is somewhere on that line and can be removed from the rest of it. — Every 1 in b3 lies in c9, so the 1 for that box is somewhere on that line and can be removed from the rest of it.

Learn these first

Hidden SingleLook at one digit in one row, column or box.

Related locked candidates

Locked Candidates Type 2 (Claiming)Inside one row or column, every spot left for a digit sits in the same box.
Locked Candidates (general form)Sometimes all the spots for a digit inside one group also sit inside a second group.

How often does it come up?

Our rough estimate: very common. Typically the first technique needed once singles stall on a medium grid.

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