This post had an old URL.
You can now find this puzzle here:
https://andrewspuzzles.blogspot.com/2019/03/sudoku-puzzle-no-357-extreme.html
*--------------------------------------------------*
| 1 689 3589 | 356 36 3568 | 7 2 4 |
|*378 2678 2378 | 2346 9 23468 |*38 1 5 |
| 4 28 2358 | 7 123 12358 | 9 368 368 |
|---------------+------------------+---------------|
| 5 279 1 | 8 4 237 | 6 39 237 |
|*789 3 4 | 126 1267 1267 | 5 *89 *278 |
| 6 278 278 | 23 5 9 | 1 4 f2378 |
|---------------+------------------+---------------|
|*389 1 3689 | 23569 236 2356 | 4 7 36-8 |
| 37 5 367 | 14 8 14 | 2 36 9 |
| 2 4 3689 | 369 367 367 |f38 5 1 |
*--------------------------------------------------*