Technique 2 of 5 · Easy boards
Confinement
When all the open cells of a color sit in one row or one column, that line's crown must be the color's crown. Everything else in the line is ruled out. It works the other way round too.
The idea
A color still needs its crown somewhere among its open cells. If those cells all lie in the same column, then whichever one gets the crown, it will also be that column's crown. A column holds only one crown, so no other cell in that column can have one.
already ruled outthe cells the step looks atruled out by this stepa crown this step places
The example
Here the crown in the green region (row 3, column 3) has already done its work, and the teal region is left with two open cells: rows 4 and 5 of column 1. You can't tell yet which of the two holds teal's crown. You don't need to. Either way, column 1's crown is teal's.
So the other open cells of column 1, rows 1 and 2 in the red region and row 6 in the blue region, can't hold a crown. Cross out all three.
The other direction
Swap the roles and it still holds. If the open cells of a row or column all fall inside one color, that line's crown is in that color, so the color's crown is used up by the line. Every cell of the color outside that line is ruled out.
How to spot it
- Look at colors with two or three open cells. Check whether they share a row or a column.
- Look at long, thin colors. A color shaped like a strip along an edge often ends up confined to its line.
- Look at nearly finished lines. When a row is mostly crossed out, check whether its last open cells are all one color.
Why it works
The color must have a crown in one of its open cells. All of them are in column 1, so the color's crown is in column 1. Column 1 can only have one crown, so it can't have another one somewhere else.
In Logic Legends
The hint calls this step Confinement and outlines the cells that are confined. Together with Last Cell, it solves every Easy board.