The case notes
Use an alternating line to claim every even digit
An alternating line can affect cells beyond the line. This one crosses eight cells of a Sudoku row, leaving one cell outside. Watch a worked example, then try the idea in a puzzle.
Put it into practice
One cell sits outside the line
An alternating line can affect cells beyond the line. This one crosses eight cells of a Sudoku row, leaving one cell outside.
Four even places on the line
The line begins with one, an odd digit. So it runs odd, even, odd, even, all the way along. Four of its cells must be even.
2, 4, 6, 8 are claimed
A Sudoku row has only four even digits: two, four, six and eight. These four line cells share a row, so they use every even digit in some order.
Last cell must be odd
The last cell is not on the line. It cannot be two, four, six or eight. We know it is odd without knowing its exact value.
Read the transcript
An alternating line can affect cells beyond the line. This one crosses eight cells of a Sudoku row, leaving one cell outside. The line begins with one, an odd digit. So it runs odd, even, odd, even, all the way along. Four of its cells must be even. A Sudoku row has only four even digits: two, four, six and eight. These four line cells share a row, so they use every even digit in some order. The last cell is not on the line. It cannot be two, four, six or eight. We know it is odd without knowing its exact value.
