In two lines the digit sits on the same two columns → erase it from the rest of those columns.
Technique 10 in the order the hint searches · difficulty Expert · up to advanced techniques
Say a 5 has exactly two possible cells in each of two rows, and those four places lie on the same two columns. The four corners make a rectangle whose diagonals cross in an X — hence the name.
Start by pairing up the lines with only two places
Fix on one digit and count its candidate cells row by row. Collect the rows with exactly two and find a pair whose column numbers match. It works identically with rows and columns swapped, so check both ways.
How the hint says it
In columns 1 and 9, every place 6 could go lies on rows 5 and 9. Either way, those two rows take one 6 each, so 6 comes off the remaining cells of both.
Either way round, the two columns take one each
If the first row's 5 is in the left column, the second row's 5 has to be in the right one, and vice versa. Either way the two columns take a 5 apiece, so no other cell in those columns can hold a 5.
The doorway to the advanced techniques. If a puzzle stalls here, Y-Wing or simple colouring is what comes next.
Puzzles that need this technique
Four puzzles with a spot where nothing moves until you use X-Wing. Press a number to play it.
- Practice 1 ·
4-7743044 - Practice 2 ·
4-9352289 - Practice 3 ·
4-6650149 - Practice 4 ·
4-6991796