| This technique borrows part of it's name from the Sudoku XWing technique, as it's results are similar. We've called this an HWing because quite often the formation looks like the letter H! |
| Look for any sequence of two numbers across any row or column, where the same sequence is repeated again in a second parallel row or column. Any other occurrence of each number before, between and after the two identifying occurrences must be painted. |
This technique works because adjacent cells are bound if one of them has to be painted (set). In this case the cell adjacent to a painted cell must be circled. Using this knowledge in the HWing, we find that at least one of the two parallel occurrences of either number must be painted, leading to necessary circling of it's adjacent cell - this in turn forces the second number in the other parallel occurrence to be painted.
We know that now in either of the parallel occurrences, both numbers of each parallel occurrence will become circled (in opposite parallel occurrences), so any other occurrence of each number outside of the parallel occurrences cannot be circled - hence they must be painted.
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