## Is There a Fish ?

Everything about Sudoku that doesn't fit in one of the other sections
daj95376 wrote:This thread seems to have a mind of its own. First ronk posted a reply and then it disappeared. Then I added two more puzzles and ronk's message re-appeared.

Sorry about that. I originally illustrated a starfish (squirmbag) claiming both eliminations r2c47<>7 ... but it actually only supported r2c4<>7. Rather than just a quick edit, I thought I'd try again for both elims with one fish.
ronk
2012 Supporter

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Joined: 02 November 2005
Location: Southeastern USA

Code: Select all
`+---+---+---+|312|67.|.54||7..|4..|.36||.46|5..|..2|+---+---+---+|.71|3..|.68||.6.|2.7|..3||..3|.6.|...|+---+---+---+|...|.2.|.4.||1.7|8..|..5||.24|7.5|.81|+---+---+---+`
For my solution of the 38 after x-wing, W-wing and kite i need an x-chain to eliminate 9 in r2c5. It would be nice to have a fish for that (also the 9's in r2c7 and r3c1 can be eliminated with templates), because after that the puzzle can be solved with (swordfish and) xy-wing.
Code: Select all
` *-----------------------------------* |  .  .  .  |  .  .  9  |  9  .  .  | |  .  9  9  |  . -9  .  |  9  .  .  | |  9  .  .  |  .  9  9  |  9  9  .  | |-----------+-----------+-----------| |  9  .  .  |  .  9  9  |  9  .  .  | |  9  .  9  |  .  9  .  |  9  9  .  | |  .  .  .  |  9  .  .  |  .  .  9  | |-----------+-----------+-----------| |  .  .  .  |  9  .  .  |  .  .  9  | |  .  9  .  |  .  9  9  |  9  9  .  | |  9  .  .  |  .  9  .  |  9  .  .  | *-----------------------------------*`
[Edit:]What i can see is a jellyfish in rows 1, 3, 4 and 9 with fin in r3c8 to eliminate 2 in r2c7 and remote fin (?) for r2c5.
ravel

Posts: 998
Joined: 21 February 2006

ravel, There is a finned Jellyfish in r1492\c1567 with fin cells [r2c23]. This eliminates <9> in [r3c1] and leaves a Locked Candidate 1 to perform eliminations [r2c57]<>9.

BTW: Your fin cell [r3c8] is also an exo-fin cell that would force [r3c1]<>9 and the Locked Candidate 1 to eliminate <9> in [r2c5].
daj95376
2014 Supporter

Posts: 2624
Joined: 15 May 2006

ravel wrote:For my solution of the 38 after x-wing, W-wing and kite i need an x-chain to eliminate 9 in r2c5. It would be nice to have a fish for that (also the 9's in r2c7 and r3c1 can be eliminated with templates), because after that the puzzle can be solved with (swordfish and) xy-wing.
Code: Select all
` *-----------------------------------* |  .  .  .  |  .  .  9  |  9  .  .  | |  .  9  9  |  . -9  .  |  9  .  .  | |  9  .  .  |  .  9  9  |  9  9  .  | |-----------+-----------+-----------| |  9  .  .  |  .  9  9  |  9  .  .  | |  9  .  9  |  .  9  .  |  9  9  .  | |  .  .  .  |  9  .  .  |  .  .  9  | |-----------+-----------+-----------| |  .  .  .  |  9  .  .  |  .  .  9  | |  .  9  .  |  .  9  9  |  9  9  .  | |  9  .  .  |  .  9  .  |  9  .  .  | *-----------------------------------*`

After daj95376's offerings, it's nice to see an easy one again.

Code: Select all
` .  .  . |  .  .  9 |  9  .  . . #9 #9 |  .  9  . |  9  .  .-9  .  . |  .  9  9 |  9 *9  .---------+----------+---------- 9  .  . |  .  9  9 |  9  .  . 9  . *9 |  .  9  . |  9 *9  . .  .  . |  9  .  . |  .  .  9---------+----------+---------- .  .  . |  9  .  . |  .  .  9 . *9  . |  .  9  9 |  9 *9  . 9  .  . |  .  9  . |  9  .  . sashimi swordfish c238\r358 plus fin r2c23, implies r3c1<>9`

... followed by locked candidates for r2c57<>9. I'm still looking for the W-wing. Again congratulations on your minimal 38
ronk
2012 Supporter

Posts: 4764
Joined: 02 November 2005
Location: Southeastern USA

I'm also puzzled about the w-wing. But I found a y-wing that together with an xy-wing solve the rest of the puzzle. Check out this post.
udosuk

Posts: 2698
Joined: 17 July 2005

My "W-wing" is the same as udosuk's y-wing, indeed a semi-remote naked pair (is there another meaning of w-wing ?), see the discussion here.
ravel

Posts: 998
Joined: 21 February 2006

Relative to the ravel.C38.m ...
ronk wrote:
Code: Select all
` .  .  . |  .  .  9 |  9  .  . . #9 #9 |  .  9  . |  9  .  .-9  .  . |  .  9  9 |  9 *9  .---------+----------+---------- 9  .  . |  .  9  9 |  9  .  . 9  . *9 |  .  9  . |  9 *9  . .  .  . |  9  .  . |  .  .  9---------+----------+---------- .  .  . |  9  .  . |  .  .  9 . *9  . |  .  9  9 |  9 *9  . 9  .  . |  .  9  . |  9  .  . sashimi swordfish c238\r358 plus fin r2c23, implies r3c1<>9`

I discovered my solver doesn't find this sashimi, a basic fish. By "basic" I mean an unfinned, or finned, or sashimi row-column fish, IOW no frankens and no mutants.

The reason? Using the same base sectors (c238), there is also a finned swordfish -- c238\r258 plus fin r3c8. Once a finned fish is recognized, the solver doesn't bother to look for a sashimi that uses the same base sectors. I suspect my basic-fish-algorithm is not the only one with this design flaw.
ronk
2012 Supporter

Posts: 4764
Joined: 02 November 2005
Location: Southeastern USA

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