My Sudoku

Hard Used from hard puzzles up.

Finned X-Wing

An X-Wing with a fin

Start from an X-Wing: a digit whose places in two rows line up in the same two columns, the corners. Here, a row has one or more places besides, all in one box: the fin.

If no cell of the fin holds the digit, the X-Wing is there, and the digit goes from the rest of the two columns. If one does, the digit goes from the rest of the fin's box.

So the cells of the two columns that are also in the fin's box, outside the two rows, lose the digit either way: remove it there. It works the same with columns and rows swapped, and when a row has only one of its two corners.

What to look for

Find two rows (or columns) that would make an X-Wing for a digit but for a place or two more in one box, then look at the X-Wing's columns inside that box.

Example

162347895895894986252517357389124679467951268367892368978938679426726526912159678367868462173589435858789354135685683678935689278935792356843678915789 112233445566778899
Finned X-Wing on 6: in rows 6 and 9, 6 appears only in columns 5 and 7 (R6C5, R6C7, R9C5, R9C7), apart from the fin R6C8 in box 6. If the fin is not 6, it is an X-Wing, and 6 goes from the rest of columns 5 and 7; if it is, 6 goes from the rest of box 6. Either way, remove 6 from R4C7.
  • The cells the technique relies on
  • Cells where it removes candidates, struck out in red

Practise it

In the app, Learn › Finned X-Wing sets exercises on real positions, then a full puzzle that needs this technique and nothing harder.

Practise in your browser