dailysudoku.com

Thanks for your input. I think you are right. It is a forcing chain, although the use of the pincers does cause it to act similarly to an XY-Chain.

+--------------+------------+-------------+
| 7 4 18 | 2 6 3 | 18 5 9 |
| 1358 589 2 | 45 14 19 | 6 7 1348 |
| 1356 569 135 | 457 8 179 | 134 2 134 |
+--------------+-- ...

Not sure how much of a hint you would like, but I see a naked pair, a hidden pair (or naked quadruple) and set of locked candidates. See below for more detail.

...

If you look at box 5, 4 is locked to row 5. This allows you to remove the 4 from r4c6 and r6c4. This should get you going again.

I'm no expert, but take a look at r6c7c8 and r8c7c8.

George's logic seems to be an "if this is this - then that is that" solution. That's like guessing.

While I see where you are coming from, isn't "if this, this and if that, that&quo ...

2)For an x-y chain - you need two pincer squares

Isn't that what I did, although with a longer chain? The pincers are are r1c8 and r7c6.

r1c8 (5) or

r1c8 (7), r1c3 (3), r3c2 (7), r7c2 (3), ...

+---------+----------------+-----------+
| 9 1 37 | 24 24 8 | 35 57 6 |
| 5 8 2 | 1 36 367 | 4 79 39 |
| 6 37 4 | 3579 39 357 | 2 1 8 |
+---------+----------------+-- ...

Take a look at r4c4, r9c4 and r9c7.