X-Wing
A digit restricted to the same two columns in two rows is eliminated from those columns elsewhere.
How it works
- 1Find two rows in which a digit has exactly two possible cells, and those cells fall in the same two columns.
- 2The digit takes opposite corners of that rectangle — either way, both columns are used up by these two rows.
- 3Strike the digit from those two columns everywhere outside the rectangle. Works with rows and columns swapped too.