Candidate 5 determines the 'wing' cells in yellow and one or other of those 5s must be true. Most of the time you won't. This idea could be extended to form any N-wing format, but the logistics are astronomical. Thank you for your interest. W-Wings are easy to spot and often very efficient.
That having been said, XY-Wing is not easy to find. In order to follow what is explained below, it is important to first understand the concept of Intersection.
Sudoku Snake Solving Technique XY Wings
XY Wings. An XY-Wing is a group of three cells, one sharing a unit with the other two, each having only 2 candidates. Consider the example on this page. Please enjoy the journey as we tackle an extreme Sudoku puzzle! Puzzle #23 will require Step 4: XY-Wings & XYZ Wings – December, Steps are relatively common techniques and are explained in the TI LIFE articles per above.
Steps are covered in detail, in Dan's book. Also see Sudoku.
Here is the first of the later. Five candidates can be eliminated.
Video: Sudoku xy wing examples of cover Sudoku Tutorial #23 / XY-Wing
Most of the time you won't. So regardless of which yellow cell is a 4, C7R2 is not a 4.
The easy principle is that each possible value of the hinge cell results in a Z value in one of the cells in the WXYZ-Wing pattern, thus leaving no room for a Z on any cell all four can 'see'. You later make the clarification when you state "We are looking for a 9 elsewhere that can see every 9 in the four cells".
This page will not only introduce Y wings, also called xy wings, but also generalize. be solved using Y wings plus perhaps techniques covered in previous blog pages.
HoDoKu Solving Techniques Wings (XYWing, XYZWing, WWing)
I find your '5-bullet' analysis of the Y-wing example a little too heavy. This is the Sudoku solving guide, teaching you a wide range of Sudoku solving techniques with practical examples and illustrations. Empty Rectangle or Hinge ; Remote Pair; Finned Fish; XY-Wing; XYZ-Wing; Aligned the remaining candidates, you are allowed to remove all digits not covered by a line.
Do you tackle a Sudoku on your cottage veranda, sailboat cockpit, or at a campsite?
Video: Sudoku xy wing examples of cover The XY Wing Part 1 Tutorial #43
This is from your Sunday daily puzzle of a Sudoku from early September. We know for sure that one of the two yellow cells is a 4.
But how could I ever find a situation like this? The other rules stay intact. You have just solved the puzzle.