Classical sudoku, and also the rule that the cells opposite to a cell containing a 1 should contain each of the numbers 1 - 9 once.

Example of such a grid:

- Code: Select all
`617|435|829`

328|976|514

495|128|736

---+---+---

531|297|468

746|813|952

982|654|371

---+---+---

159|782|643

274|369|185

863|541|297

Puzzle - based on another grid:

- Code: Select all
`.86|...|...`

25.|..6|4..

...|...|.3.

---+---+---

...|...|...

.4.|.1.|6..

...|4..|3..

---+---+---

3..|9..|..1

9..|...|...

...|1..|2..

In this case - the additional constraint is only implemented by singles.

I wonder what kind of solving techniques may be aimed at here.