The next simplest rule after the rule of elimination (see the last entry) is *uniqueness* (another name would be the *pigeonhole principle* ). This principle says that if there's only one place (the pigeonhole) to put a number (the pigeon), it must go there.

Consider the following puzzle:

The rule of elimination can get us this far:

Here's where the rule of uniqueness comes in. Looking at the pencil marks in the top row, we see that there is only one place for a 6 to go. Since every number must appear somewhere in every row, we know the 6 must go there. Similarly, there is only one place for a 9 to go in the 2nd row, and one place for a 3 in the 5th row.

Filling in these cells, we can perform an additional round of elimination. Some more unique cells pop up, such as the 5 in the 5th row. Earlier, there were two possible places for a 5 in that row, but one of those places was the only place for a 3. Thus, the 5 must belong in the other cell.

Now uniquess gives us a 4 and a 9. A bit more elimination, and we‘re done!

Pois e realmente um programa maravilhoso ver o desfile de 20 de setembro em Piratini. Em 2007 eu fui pela primeira vez assisti-lo e fiquei emocionada, e um desfile muito lindo feito com alma por cada um daqueles gauchos que la vivem. Vale a pena.

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