StrmCkr, I'm still going through your thorough replies, and I have a few comments about what you said about fishes:

StrmCkr wrote:you really should read up on obiwans approach to fish finding, it has huge implications as a manual solver and makes complicated fish actually easy.

Can you link to that? I only know one "easy" approach to fishing and it's this:

http://forum.enjoysudoku.com/a-new-view-of-fish-naked-or-hidden-t5017.html?hilit=fish%20subsetsIt does make finding (normal) fishes a lot easier, but it's a lot of work to convert the rows and columns into subset format, which cancels the benefit from my point of view. That's why I don't fish almost at all, even though it would sometimes provide effective openings. I've even made some improvements to that method to make finding finned and sashimi fish easier, but I still don't use it, because it's so tedious and the findings are uncertain. Software would considerably help here, but that would break my pencil-and-paper purism.

So, is there an *actually* easy way to find normal fishes manually? If not, I prefer to use a few more chains to work around them, which has worked so far.

for example x-cycles wont find the finned x-wing below.

Finned X-Wing: 2 c28 r25 fr1c2 fr3c2 => r2c13<>2

You mean Hodoku doesn't find it, because it doesn't have X-Cycles? If it did, it would. You just need to use a grouped X-Cycle:

Discontinuous Grouped X-Cycle Type 1: (2)r2c13-r2c8=r5c8-r5c2=r123c2-(2)r2c13 => -2 r2c13

Here's the X-Chain version the same:

X-Chain (Grouped Skyscraper): (2)r2c8=r5c8-r5c2=(2)r123c2 => -2 r2c13

bigger fish can be seen and written as chains: several users are very good at converting and posting large fish logic into chain notation

SpAce wrote:Can you link to any examples? I'd really like to see how it's done. For example, a swordfish with vertices spread into 9 boxes doesn't have any native strong links to work with.

Here is an unfinned mutant jellyfish (4-fish) from #61 of the top1465...

http://forum.enjoysudoku.com/post37073.html#p37073

Thanks for the example, though I guess I didn't pose my question clearly. I'm not an expert on mutant fishes but I've understood that they can usually (always?) be expressed as grouped chains, so I wasn't referring to them when I talked about "bigger fishes that can't be seen as chains". Clearly some bigger fishes can be expressed as chains, especially mutant ones, but that doesn't prove anything about all of them. I'm still pretty sure that some aren't easily converted into chains, and that was my original point. Do you know anyone who can chain a normal 3-3-3-Swordfish spread into 9 boxes?

Mutants are easier to see as chains because their box-based nature typically provides strong links through grouping. That's why I haven't bothered to study them much. Even if I understood them completely, finding the corresponding chains would be much easier and more intuitive for me. I'm more interested in fishing methods for the normal (row/col) fishes which don't seem to have simple chain counterparts.