They said that numbers 1-9 would be used, but there is no one to say that 1-9 will appear only once in the circles
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Wrong! They said that 1-9 will only appear in each SET! We don't know what a SET is. So, LOGICALLY, we don't even know if 1-9 will only appear once in each row/column! By your logic, we all could be doing it wrong.
the 1x2x3 thing is wrong anyway, look at the first circle, if you put a 1 in it, to get 8 horizontally the box alongside needs to be a 7 and the vertical sum with the 7 in it is 14, which means you need another 7 which you cant do. *wipes forehead*
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Maybe the entire puzzle was made just to stray us from thinking about the obvious? That could explain the error in the upper left corner, eh?