Norten29 wrote:Does anyone know a better, or more extensive rule for hidden pairs?
The description Angus gives is correct. Perhaps some examples will help.
Here are 9 cells in a row:
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[12345][12567][<>12]|[<>12][<>12][<>12]|[<>12][<>12][<>12]
The first two cells have 5 candidates including a '1' and a '2'. The next 7 cells can have anything at all other than a '1' or a '2' (I'm using '<>' to mean 'not'). So there are TWO candidates that only appear in TWO cells. The only possible results are that either the first cell is 1 and the second is 2 OR the first cell is 2 and the second is 1. Either way, no other candidate can exist in the first two cells, leaving you with:
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[12---][12---][<>12]|[<>12][<>12][<>12]|[<>12][<>12][<>12]
Hidden triples take it a step further:
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[12345][12356][12356]|[<>123], etc.
[12345][12356][12-56]|[<>123], etc.
[12345][1-356][12-56]|[<>123], etc.
[-2345][1-356][12-56]|[<>123], etc.
In each of these four cases, the digits 1, 2 and 3 appear ONLY in the first three cells -- so the first three cells are full -- all other candidates are eliminated:
[EDIT: type corrected]
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[123--][123--][123--]|[<>123], etc.
[123--][123--][12---]|[<>123], etc.
[123--][1-3--][12---]|[<>123], etc.
[-23--][1-3--][12---]|[<>123], etc.
THREE candidates appearing in only THREE cells.