## Sashimi and finned fish

Advanced methods and approaches for solving Sudoku puzzles

### Sashimi and finned fish

What is the difference between a sashimi fish and a finned fish of the same size?
Once upon a time I was a teenager who was active on here 2007-2011
ocean and eleven should have paired up to make a sudoku-solving duo called Ocean's Eleven
999_Springs

Posts: 399
Joined: 27 January 2007
Location: In the toilet, flushing down springs, one by one.

### Re: Sashimi and finned fish

999_Springs wrote:What is the difference between a sashimi fish and a finned fish of the same size?

Code: Select all
`8....25...429...7..1......9.2.57...3...2.1...1...93.4.2......5..5...843...83....6 # wapati puzzle`

Every basic fish pattern (above 1-Wing) has at least two vertices in every row/column of the fish. In the Swordfish below, there are at least two asterisks (*) in each row/column for the Swordfish. Since all of the extra cells (#) in the Base Sectors [r249] are contained in [b3], then this pattern qualifies as a finned Swordfish ... and all eliminations are restricted to [b3].

Code: Select all
`# finned Swordfish r249/c578 w/fin cell [r2c9]*-----------------------------------*|  .  .  .  |  1  1  .  |  . -1  .  ||  .  .  .  |  . *1  .  | *1  . #1  ||  .  1  .  |  .  .  .  |  .  .  .  ||-----------+-----------+-----------||  .  .  .  |  .  .  .  | *1 *1  .  ||  .  .  .  |  .  .  1  |  .  .  .  ||  1  .  .  |  .  .  .  |  .  .  .  ||-----------+-----------+-----------||  .  .  1  |  1  1  .  |  1  .  1  ||  .  .  1  |  1  1  .  |  .  .  1  ||  .  .  .  |  . *1  .  | *1 *1  .  |*-----------------------------------*`

If I perform a (definitely invalid) modification to this pattern, then I get a Sashimi Swordfish because there is now only one cell with an asterisk (*) in [c8] from the Swordfish pattern.

Code: Select all
`# Sashimi Swordfish r249/c578 w/fin cell [r2c9]*-----------------------------------*|  .  .  .  |  1  1  .  |  . -1  .  ||  .  .  .  |  . *1  .  | *1  . #1  ||  .  1  .  |  .  .  .  |  .  .  .  ||-----------+-----------+-----------||  .  .  .  |  . *1  .  | *1  .  .  ||  .  .  .  |  .  .  1  |  .  .  .  ||  1  .  .  |  .  .  .  |  .  .  .  ||-----------+-----------+-----------||  .  .  1  |  1  1  .  |  1  .  1  ||  .  .  1  |  1  1  .  |  .  .  1  ||  .  .  .  |  . *1  .  | *1 *1  .  |*-----------------------------------*`

Some people call this a finned Sashimi Swordfish because of cell [r2c9], but the qualifier term finned isn't appropriate -- even though some of us include it anyway.

Bottom Line: I should have kept my mouth shut and let those who are much more knowledgeable answer your question.
daj95376
2014 Supporter

Posts: 2624
Joined: 15 May 2006

I'd like to point out that the "altered" example is actually two overlapping Sashimi Swordfish and there were more eliminations available.
Either "#1" could be the Sashimi, it is reasonable to take advantage of both.

Code: Select all
`*-----------------------------------* |  .  .  .  |  1  1  .  |  . -1  .  | |  .  .  .  |  . *1  .  | *1  . #1  | |  .  1  .  |  .  .  .  |  .  .  .  | |-----------+-----------+-----------| |  .  .  .  |  . *1  .  | *1  .  .  | |  .  .  .  |  .  .  1  |  .  .  .  | |  1  .  .  |  .  .  .  |  .  .  .  | |-----------+-----------+-----------| |  .  .  1  |  1  1  .  |  1  . -1  | |  .  .  1  |  1  1  .  |  .  . -1  | |  .  .  .  |  . *1  .  | *1 #1  .  | *-----------------------------------* `

Similarly one can consider a skyscraper to be two overlapping x-wings and we do take advantage of both.

Code: Select all
`*-----------------------------------* |  .  .  1  |  x  x  .  |  .  .  .  | |  .  .  .  |  .  .  .  |  .  .  .  | |  x  x  .  |  .  .  1  |  .  .  .  | |-----------+-----------+-----------| |  .  .  .  |  .  .  .  |  .  .  .  | |  .  .  .  |  .  .  .  |  .  .  .  | |  .  .  .  |  .  .  .  |  .  .  .  | |-----------+-----------+-----------| |  .  .  .  |  .  .  .  |  .  .  .  | |  .  .  .  |  .  .  .  |  .  .  .  | |  .  .  1  |  .  .  1  |  .  .  .  | *-----------------------------------*  `

Edited to correct skyscraper eliminations at r1c6 and r3c3.
These must be left to allow finned-x-wing patterns.
wapati
2010 Supporter

Posts: 527
Joined: 13 September 2006

### Re: Sashimi and finned fish

999_Springs wrote:What is the difference between a sashimi fish and a finned fish of the same size?

Were all the fin cells false, if a fish is reducible then the fish is 'sashimi.' If an unfinned fish of the same size remains then the fish is 'finned.'
ronk
2012 Supporter

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