Getting the puzzle ready for you…
How to solve sudoku 4 of 6
Now you look at one digit across several rows at once. If two rows can only place that digit in the same two columns, it is taken in those columns. With three rows it’s called a swordfish, with four a jellyfish — the same idea, one size bigger.
Take one digit. In two rows it can only go in exactly the same two columns — four squares on the corners of a rectangle. However you fill it in, the digit is taken in those two columns, so it drops out elsewhere in those columns. It works just as well with rows and columns swapped.
An X-wing with three instead of two: in three rows a digit only fits in the same three columns. Each row takes one, so in those columns the digit is gone everywhere else. Not every row has to offer all three columns — two is enough.
The same fish one size bigger: four rows that can only place a digit in the same four columns. In those columns the digit drops out everywhere else.