July 17 -- is this a fish?

[David Bryant]

After doing the more or less usual stuff I arrived at this position.

Code: Select all

  35    45    9     2     47+   6     37-   1     8
  34    7     18    19    5    148    39    6     2
  28   126  1268   179    3   1789    4     79+   5
  6     29    27-   3     1     5     79+   8     4
  1     3     4     6     8     79+   2     5     79-
 578    59   578    4     79    2     6     3     1
  9    146    3     5     2     17    8     47    67+
  47    8     17*  179+   6   13479   5     2    379*
 257  2456  2567    8    479    37    1    479   367*

I was able to eliminate "7" from r8c3, r8c9, and r9c9 by reasoning as follows.

A. r4c7 = 7 ==> r3c8 = 7 ==> r1c5 = 7 ==> r5c6 = 7 ==> r8c4 = 7

Also, r3c8 = 7 & r5c6 = 7 ==> r7c9 = 7

B. r4c7 <> 7 ==> r1c7 = 7 & r4c3 = 7 & r5c9 = 7

See the + and - signs in the grid above to see how this works. After making the eliminations of "7" the rest of the puzzle is easily solved.

Here's my question. Is this some species of "fish"? In a way this looks like a fishy pattern, but it's not quite as simple as tracing out a binary chain. One of the "colors" (the + signs) is mapped out sort of like a Nishio move -- the other "color" is just a regular binary chain. Anyway, I've been able to spot patterns like this in quite a few puzzles, but I have no idea what it ought to be called. dcb

[Ruud]

Hi David,

there are multiple fish in this puzzle and there is no need for Nishio.

Your grid:

Code: Select all

  35    45    9     2     47    6     37    1     8 
  34    7     18    19    5    148    39    6     2 
  28   126  1268   179    3   1789    4     79    5 
  6     29    27    3     1     5     79    8     4 
  1     3     4     6     8     79*   2     5     79* 
 578    59   578    4     79    2     6     3     1 
  9    146    3     5     2     17*   8     47#   67*
  47    8     17   179    6   13479   5     2    379- 
 257  2456  2567    8    479    37    1    479   367-

You can see a finned X-Wing. The 4 starred cells almost form an X-Wing, but the fin (#) prevents it, so either the X-Wing exists or the fin must contain digit 7. In both cases, the candidates 7 in R89C9 are gone.

There is a finned jellyfish in 7 that can be found after these eliminations and a finned X-Wing for digit 9.
The finned X-Wing is a pattern that is not hard to spot. Finned jellyfish is just as difficult to find as the unfinned species.

cheers,
Ruud.

[Steve]

The fewest number of fish I can identify to make David’s eliminations from his grid is three:
(a) The X-wing for 7 based on rows 5 and 7 (columns 6 and 9; box 9) eliminates from r8c9 and 9c9.
(b) The swordfish for 7 based on rows 1, 4 and 6 (columns 5 and 7; box 4) eliminates from r9c5.
(c) The swordfish for 7 based on columns 1, 4 and 5 (rows 6 and 8; boxes 2 and 7) eliminates from r8c3. This elimination requires (b) to be applied first

Perhaps two fish will serve. As Ruud says, the grid is full of sea life.

Steve