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[daj95376]

[storm_norm]

Danny,
I am going to try and take a new approach to this puzzle.
the chain that results is very very long.

in this puzzle, if you remove the 9 from r1c8, you are left with {3,7}.
that {3,7} cell completes this w-wing
(3=7)A - (7)B = (7)C - (7=3)D which would eliminate the 3 in r1c5.
can this partial chain be made?
w-wing{3,7} = (9)A...

[daj95376]

Norm,

Your chain may be perfectly valid, but I'm not the one who would know for sure. I've always been uncomfortable with embedded sub-patterns, even though I've seen some that've knocked my socks off once I convinced myself that they worked.

I agree with your elimination, but that's because I see it as two chains with the strong link on <3> in [r1] resulting in contradictions when [r1c8]=7|9.

Specifically:

[r1c8]=7 should force [r1c5]=3, but instead forces [r3c4]=3 by following the W-Wing cells. This results in a contradiction by adding (3)r3c4-(3)r1c5=(3)r1c8.

[r1c8]=9 should force [r1c5]=3, but your =(9)A chain instead forces [r6c5]=3. This results in a contradiction by adding (3)r6c5-(3)r1c5=(3)r1c8.

This then leaves [r1c8]=3 to crack the puzzle.

BTW: As individual chains, [r1c8]<>7|9 can be had with shorter chains.

[tlanglet]

Three steps:

[Marty R.]

I used simple coloring on 7. Then in the rightmost stack there was an XY-Wing Chain, 27-26-26-26-67. It was flightless but a pincer transport removed the 7 from r5c6 and finished the puzzle.