999_Springs wrote:I usually try to find strong links and see if they turn into X-wings, swordfish, etc. This seems to work well with X-wings and 2x2x2 or 2x2x3 swordfish. But for the bigger ones I don't have a method of finding them manually which works well and just have to stare at the puzzle and see if any pop out before my eyes.
Arcilla introduced a new view of fish here:
http://forum.enjoysudoku.com/viewtopic.php?t=5017&start=0&postdays=0&postorder=asc&highlightI wasn't aware of her post when I introduced the rn- and cn- spaces in my book and later in a few posts in connection with hidden chains (e.g. here
http://forum.enjoysudoku.com/viewtopic.php?t=5555).
In the proper rn- or cn- space, a fish looks like a naked Subset.
The rn- and cn- spaces can be considered as a formalisation and a generalisation of Arcilla's view.
They are defined formally in my book and less formally in these threads:
http://www.sudoku.org.uk/SudokuThread.asp?fid=4&sid=9235&p1=2&p2=10http://forum.enjoysudoku.com/viewtopic.php?t=5555In my book and on my web pages, you can find an extended Sudoku board including these spaces. You can also find a method for using them systematically. This can be helpful for finding fish and other patterns.
rn and cn spaces are implemented in Ruud's Sudocue program, so that you don't have to compute them manually.
As the rn- and cn- spaces are the representation of generalised logical symmetries, they can be used for finding much more than fish, e.g. hidden xy, xyt and xyzt chains.
