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[arkietech]

[Marty R.]

[arkietech]

[keith]

This needs some kind of chain. You might try R9C1 = 8 => R5C1 = 8 via the 34 pair in C5.

Keith

[nataraj]

what I see is

a w-wing (3) r4c7=r9c9 via col 8
another w-wing (4) r1c7=r3c6 via col 3

AND a sort of grouped m-wing involving the marked cells in col 1, which sets r9c789<>3.

How?

if r9c5<>3 then r9c5=4 then (strong link (4) in col 1) r7c1=4 then r7c78=3 which means at least one of r9c5 and r7c78 must be "3"

In fact, if you apply the 2 w-wings, the (regular, not grouped) m-wing (3) r9c5=r7c8 (via col 1) appears.

_________

edit: in case anybody wonders about the m-wing reference, this is how I think:

any time a bi-value cell (in this case r9c5 {3,4}) "sees" a strong link in one of the two candidates of the bi-value (r7c1 and r9c1 in "4"), check for a strong link in the other candidate (here: "3") and coming out of the other end of the (first) strong link (that would be r7c1). In dan's grid this strong link (3) is between r7c1 and r7c78. r9c5 and r7c78 are the two pincers of the wing, r9c789 the victim cells

P.S. If you don't like to use the term m-wing, just call it the "nataraj gun" www.dailysudoku.com/sudoku/forums/viewtopic.php?t=2908"

[daj95376]

There are some XY-Chains, but none of them seem to advance the solution much.

There are three chains that crack this puzzle. One produces [r7c1]<>3, the second produces [r9c1]<>8, and the third is a generalized M-Wing for [r7c7]<>8.

[Correction: nataraj's grouped M-Wing is chain #4.]

[arkietech]