After solving as many cells as possible with naked singles, the next step is to look for a number in an unsolved cell
where the other instances of this number in the same box are prohibited because they see the same number in their rows
and columns. Using the same puzzle used in the naked singles help page, focus on r7c1. The 3 is the only instance in box7.
This has resulted because of the given 3s at r3c3 and r6c2 prohibit a 3 being placed in the cells r789c2 and r789c3,
leaving r7c1 the only place for it to go.
Notice also that the 6 at r9c2 is the only 6 in box 7 as a consequence of the given 6s at r5c3 and r7c7 and the solved
6 at r8c6. Also the 6 at r6c9 is the only 6 in box 6 due to the given 6s at r5c3 and r7c7 and the solved 6 at r4c4. Taking
this process as far as possible leads to the following grid: