The Ultimate FISH Guide

Advanced methods and approaches for solving Sudoku puzzles

Re: The Ultimate FISH Guide

Postby StrmCkr » Sun Feb 18, 2018 9:08 pm

After some though the word eventual for canabaliatic eliminations refers to a subset smaller fish eliminating the base candidate in the larger fish... So current fish model won't hit these eliminations directly. As per previous post.
Some do, some teach, the rest look it up.
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Re: The Ultimate FISH Guide

Postby sultan vinegar 2 » Fri Feb 23, 2018 10:29 am

Firstly, I am 'sultan vinegar', but I have lost my old account details (moderators, I'm guessing we can't merge these accounts given I appear to have no way to prove I really am sultan vinegar?)

Secondly, I have not looked at sudoku for a couple of years, but this recent interest in fish reminds me of my post a couple of pages back which I never followed up:

sultan vinegar wrote:One thing that I think is missing from the exemplars is rank 2 fish eliminations. I remember a while ago coming up with an extended list of fish exemplars; I think I had everything up to jellyfish size, basic, franken, mutant, finned, Siamese (like a skyscraper, not the Hodoku definition) and rank 2 fish. Then I got distracted by exocets. Ironically, my current thinking on exocets has been interrupted by these fish! I'll try and find my exemplars and post them, as I'm sure I would have missed some.

Given this fish guide appears to be in the process of significant revision, I will dig-out my old extended list of exemplars and post them in the next day or so. From memory, I used some different symbols to those used in the original guide because there are some additional concepts in my guide, but it shouldn't be a problem to come up with an agreed notation for any revision to this guide.

My advice to anyone learning about fish is that because the fish concept developed in an ad-hoc way as new fish concepts were found, some definitions are duplicates or redundant. Note I only found sudoku after the 'glory years' when this forum was at its peak. Most of the key contributors to this forum had moved on by then, but I was able to cherry-pick this excellent guide and sort out the different concepts in my own mind.

Finally, having studied fish extensively, I am happy to contribute to the revision of this guide and answer any questions others have about fish, although I'm sure I will need to refresh my own knowledge along the way given its been a couple of years.

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Re: The Ultimate FISH Guide

Postby tarek » Fri Feb 23, 2018 7:39 pm

Hi SV and SV2 ,

I would advise any new fisherman to read the 1st post of this thread. Even in its current un-revised form would have more precise and Un-duplicated info. I would also advise therefore not to read anywhere else 8-)

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Preliminary thoughts

Postby sultan vinegar 2 » Mon Feb 26, 2018 6:22 am

Below are my preliminary thoughts prior to posting exemplars in batches beginning with cyclops fish. Feedback (both good and bad) on the proposed structure is most welcome. It will be interesting to see how the revisions to this guide are received.

  • All Sudokus can be solved in one step with a giant net; the restriction to considering the subset of a single digit (also known as a floor) only is a natural simplification especially for human players.
  • The intention of this revised guide is to cover all single digit/floor eliminations, of which it may be argued that fish are one type, with other types being singles, locked candidates, x-chains (both open and closed, both grouped and ungrouped), and (single digit) Kraken fish.
  • In their general form, fish represent nets, the simplest fish net being the swordfish made from three rows and three columns. Note some of these nets may be linearised to x-chains with the use of derived inferences, but others are unable to be simplified and remain as nets. Each player will have their own philosophy along some spectrum as to what methods constitute acceptable solving. Personally, I class these fish nets in the same category as Exocets; they comprise a subset of well defined patterns that human players are able to recognise, understand, and utilise.
  • A difficulty with cataloguing a fish aquarium is that many accepted fish concepts change depending on how you look at the same fish; a situation that is not ideal for making robust definitions. These concepts include:
    • Base and cover sets
    • Fish size (e.g. swordfish vs jellyfish)
    • Fish shape (e.g. franken vs mutant)
    • Fins (e.g. exo-fins, endo-fins, remote or dorsal fins, whether a candidate is a fin or not)
    • Degeneracy (e.g. sashiminess, remora fish, cannibalism, Siamese fish)
  • Another difficulty is that these accepted concepts were developed in an ad-hoc manner as new fish were discovered. Some of these concepts don't generalise well to more complex fish, and become redundant. If what is known about fish today was known from the start, things would be defined quite differently and be simpler to understand, but to some extent we remain bound to these legacy definitions.
  • The intended structure of the guide is to consider one fish at a time, starting from the simplest and moving to the more advanced, noting the concept of simplicity is not able to be rigorously defined due to the points made above, and as such will be a personal opinion, chosen to make the tutorial as logical to follow as possible. This structure works particularly well for the fish at the beginning of the guide where it is common for one new concept to be introduced per fish. Each fish in the guide will:
    • Introduce a new fish concept if required, noting some fish may require multiple new concepts to be introduced together, while others may require no new concepts
    • Have the pattern defined with a template
    • Prove the logic of the elimination(s)
    • Be accompanied by a real example
    • Contain the nomenclature for how to notate the elimination(s)
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Re: The Ultimate FISH Guide

Postby David P Bird » Wed Mar 21, 2018 10:32 am


Is this re-working dead or is it just all collaboration is being conducted via private messages/e-mails? As exotic fish are not my forte and some of my views are contentious, I've been happy to be one of the indians rather than a chief here, but in the hope that this project has not been abandoned, here are a few selected thoughts.

I am all for tidying up the fish descriptions as, frankly, the plethora of fancy terms is quite a burden for newcomers to absorb, and their payback in terms of extra puzzles that can be solved isn't that great.

In the Sudpedia Mirror a 'floor' is defined as "A part of the grid containing 3 rows and 3 boxes" so there's a clash. (I just call your floors digit maps.)

I favour simply treating the body of a fish as a one Boolean and the set of fin cells as another. In this way, whatever eliminations they provide can be notated as an AIC showing any additional links used. This eliminates the need to define kraken fish, remote fins, endo-fins etc. This view seems to agree with yours but I'm not certain.

This also applies to rival fish that have common eliminations that I also look for. I guess these could be combined into some sort of exotic fish but they would still need to be explained, so I've never tried.

When a fish has a single fin and a single potential elimination that see each other they can both be eliminated in a single step, but this is awkward to notate. One approach is to use an 'and so' construct:
(x)Fish:Cells = FinCell => PE cell <> x, &So => FinCell <> x

In addition to the examples that are planned, I also think that tips to help manual players to find fish would also be useful.

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