Inside a box the digit sits on one line only → erase it from that line outside the box.
Technique 6 in the order the hint searches · difficultyVery hard · up to intersections and triples
Say a 4 could go in two or three cells of some box, and all of them lie on the same row. The 4 has to appear somewhere in that box, so it ends up on that row one way or another.
Take one box and check where each digit can sit
Split a box's nine cells into its three lines and look for a digit whose candidates all crowd into one of them. The three cells where box and line overlap are this technique's stage. You only have to study one box, so it gets fast with practice.
This is how the hint puts it
In the top-centre box, every place 8 could go lies on row 1. 8 has to appear somewhere inside that box, so it comes off the rest of that row outside the box.
The box claims one seat on that line in advance
It is settled that the 3 goes inside the box. Since every place for it lies on column 2, the 3 lands in one of those three cells of column 2 — which means the other six cells of column 2 cannot have a 3.
Needing this much makes a puzzle Very hard. It's the first technique that looks at a box and a line together, and your field of view widens a step.
Puzzles where this technique decides it
Four puzzles that won't give up the next move until you reach Pointing Pair. Press a number to open it.
- Practice 1 ·
3-9435761 - Practice 2 ·
3-8871522 - Practice 3 ·
3-8307283 - Practice 4 ·
3-7743044