Practise: XY-Wing
This puzzle is picked so that the easy moves run out and exactly the XY-Wing gets you going again. Solve as far as you can — when nothing obvious is left, the pattern is waiting for you.
Skip the obvious cells and start right where the technique is needed.
How to spot it
Look for cells with exactly two candidates. For each, check the cells it sees for two more bi-value cells that share one digit with it and one digit with each other. The shared digit of the two wings is the one you eliminate, in cells seeing both wings.
Put it to use
Where you will meet it
Hard grids are built around moves like this one. That is where it earns its keep.
Play HardStuck on a grid of your own?
Type the position into the solver and it walks the whole solution, naming the technique behind every step — including this one.
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