| Sudoku Tutorial |
| Hidden Singles |
Hidden single: When a candidate is present only one time in a house, if that cell contains more than one candidate, it is a HIDDEN SINGLE. In row 5, candidate 3 is only present once (r5c1). This eliminates the 7 and changes the cell to a naked single (3). (In this example, the 3 is also a hidden single for box 4)  |