The New Sudoku Players' Forum

[Yogi]

.83..6.........63..1.3.8.9.......4.6.962.718.7.8.......2.8.9.6..69.........7..91.

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+---+---+---+
|.83|..6|...|
|...|...|63.|
|.1.|3.8|.9.|
+---+---+---+
|...|...|4.6|
|.96|2.7|18.|
|7.8|...|...|
+---+---+---+
|.2.|8.9|.6.|
|.69|...|...|
|...|7..|91.|
+---+---+---+


[P.O.]

basics:

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( n6r9c5   n6r6c4   n6r3c1   n7r7c3   n7r4c8   n7r2c2   n8r8c7
  n8r4c5   n8r2c9   n9r6c9   n9r4c4   n1r1c9   n1r4c3   n2r4c1
  n7r8c9   n8r9c1 )


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r5c9{n5 n3} - b4n3{r5c1 r46c2} - r9n3{c2 c6} - r4c6{n3 n5} => r5c5 <> 5

5r5c19 => r3c3 r9c9 <> 4
 r5c1=5 - c2n5{r46 r9} - r9c3{n5 n4}
 r5c9=5 - b6n3{r5c9 r6c7} - c7n2{r6 r13} - r3c9{n25 n4}


bte:

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SWORDFISH ROW: n4 (3 5 7) (1 5 9)
(((1 1 1) (4 5 9)) ((1 5 2) (2 4 5 7 9)) ((2 1 1) (4 5 9))
 ((2 5 2) (1 2 4 5 9)) ((6 5 5) (1 3 4 5)) ((8 1 7) (1 3 4 5))
 ((8 5 8) (1 2 3 4 5)))

( n4r2c3   n5r9c3   n2r3c3   n2r9c9 )

intersections:
 ((((5 0) (4 2 4) (3 5)) ((5 0) (6 2 4) (3 4 5)))
 (((3 0) (7 7 9) (3 5)) ((3 0) (7 9 9) (3 4 5)))
 (((2 0) (1 7 3) (2 5 7)) ((2 0) (1 8 3) (2 4 5)))
 
ste.


[Yogi]

Thank you. I take it that you have got to here:

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+-------------------+-------------------+-------------------+
| 459   8     3     | 45    24579 6     | 257   245   1     |
| 459   7     245   | 145   12459 1245  | 6     3     8     |
| 6     1     245   | 3     2457  8     | 257   9     245   | /***********
+-------------------+-------------------+-------------------+
| 2     35    1     | 9     8     35    | 4     7     6     |
| 345   9     6     | 2     345   7     | 1     8     35    |
| 7     345   8     | 6     1345  1345  | 235   25    9     |
+-------------------+-------------------+-------------------+
| 1345  2     7     | 8     1345  9     | 35    6     345   |
| 1345  6     9     | 145   12345 12345 | 8     245   7     |
| 8     345   45    | 7     6     2345  | 9     1     2345  |
+-------------------+-------------------+-------------------+


I’m trying to follow your first line of logic. If you are starting with the assumption that r5c9 is NOT 5, then I read it as (5=3)r5c9 – 3r5c1=r46c2=3r9c2
which (ignoring any errors in my Eureka) says that when r5c9 is not 5, it’s 3, so r5c1 is not 3, r4c2 or r6c2 is 3 and r9c2 is not 3.
This leaves r9c23 as (45) and r9c69 as (23).
How do you get from there to r5c9 <> 5, please?

[P.O.]

hi Yogi,

from here: when r5c9 is not 5, it’s 3, so r5c1 is not 3, r4c2 or r6c2 is 3 and r9c2 is not 3.

i use the premisse that r5c9=3 so n3 in r9c9 is eliminated so r9c6=3 then r4c6=5 and i conclude that r5c5<>5 which makes possible the second chain.

[eleven]

Yogi, you have to know that in PO's (and Denis') notation you might have to memorise all earlier nodes - and it will not tell you, which ones.
Here you have to memorise the 3 in r5c9 to understand the link r9n3{c2 c6}.
(5=3*)r5c9 - r5c1 = r46c2 - r9c2 = *3r9c6 - (3=5)r4c6
An easy way to follow such chains is to use a simple solver, which does the memorising for you. (click on 3r5c9, which eliminates it from r5c1 and r9c9, use the locked candidate in r46c2 to eliminate it from r9c2, then only 3r9c6 is left in r9 ...)

[Yogi]

Jeez – total stuff-up!
I see now that your chain eliminates the 5 at r5c5 (not r5c9) which allows the second chain.
Something I found interesting while working on this:
3r5c9 => 2r9c9
|
5r5c9 => 2r9c9

So 2 can be placed at r9c9, but that was not enough for me to solve it.

Thanx!

[Cenoman]

Trying to catch P.O.'s solution, I have noticed that in his "bte" , a swordfish on the 4s is encompassed.
So, inspired by his findings, here is another two stepper (w/o any complex elimination of 4r3c3):

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 +---------------------+------------------------+---------------------+
 |  59-4   8     3     |  45    24579   6       |  257   245   1      |
 |  59-4   7     245   |  145   12459   1245    |  6     3     8      |
 |  6      1     245#  |  3     2457*   8       |  257   9     245*   |
 +---------------------+------------------------+---------------------+
 |  2     c35    1     |  9     8      a35^     |  4     7     6      |
 | d345*   9     6     |  2     34-5*   7       |  1     8   ea35^    |
 |  7     c345   8     |  6     1345    1345    |  235   25    9      |
 +---------------------+------------------------+---------------------+
 |  1345*  2     7     |  8     1345*   9       |  35    6     345*   |
 |  1345   6     9     |  145   12345   12345   |  8     245   7      |
 |  8     b345   4+5   |  7     6      a2345^   |  9     1    a2345^  |
 +---------------------+------------------------+---------------------+

1. Finned Swordfish (4)r357\c159, fin r3c3 =>-4r12c1; NP(59)r12c1 => -5 r23c3, +5 r9c3
2. Almost W-Wing [(5=3)r4c6 - r9c6*=*r9c9 - (3=5)r5c9] = (3)r9c2 - r46c2 = r5c1 - (3=5)r5c9 => -5 r5c5; ste
(Note: my step #2 is the same as P.O.'s step #1)