Feedback and Questions

Yes I had changed the solver, see
/Whats_New

But didn’t realise it had a knock on effect on the printing. Fixed now. Thanks for the alert

Clear your cache and reload. I've made a new version which I'm quite excited about. "Chaining strategies that report chains now display those chains as a new graphical element on the big board"

Its possible the problem is the new graphics library but I build the new version in Firefox - you using Firefox?

Best regards

Awesome, that’s good news :)

Tried hard to be as widely browser compatible as possible

Yes. But I need examples to improve it. I can make the puzzles myself and I do solve > 99% of them so I didn't think I was very far off. Would it be possible to send me your next unsolveable, say a screen shot?

This is a very interesting area and its quite philosophical. I would distinguish between a) the 'pattern' that is found that a strategy uses to eliminate candidates (logically) and b) finding that pattern in the first place. All the documented strategies assume you can find the opportunity and they are all logical apart from the last two (which I place under the heading 'trial and error'). However, there is little help for the solver in how to find them apart from simple rules like - look for bi value (2 candidates in cell) and bi-location (two candidates in a unit) situations (since these lead to chains which are the building blocks of many strategies).

When searching for opportunities to apply strategies your path is determined by all the dead ends and in a sense these are the 'errors'. A computer has to look at every single dead end because it doesn't have a mind. But in order for a human or a computer not to take years solving a puzzle, we use logical optimizations. Even your 'random' search is not really random (trial) because you intelligently select what seem to be the best opportunities first.

Where I draw the line - because the whole 'trial and error' vs determinism - is blurry - is whether a strategy changes the board to get an answer. Nishio and Bowmans bingo do this, as does Crook fundamentally. By this I mean "If I remove/add a number here - what is the consequence?". A 'pattern' based strategy is, imho, is on the other side of the 'trial and error' divide. It asks the question "because X or Y is present/absent, what is consequence of that?"

I hope that stab at rephrasing helps and I've not repeated myself.

+---------------+------------------+--------------+
|    3   9    2 |      7    46   8 |   46   5   1 |
|    7   6    5 |      2    14 134 |   34   8   9 |
|    8   4    1 |   3569   569  35 |   36   7   2 |
+---------------+------------------+--------------+
|    6   7    3 |     45    45   9 |    1   2   8 |
|    1   5    9 |     38    28  23 |    7   6   4 |
|   24  28   48 |      1     7   6 |    9   3   5 |
+---------------+------------------+--------------+
|  249 128  478 |    489     3  47 |    5  14   6 |
|   49  18 4678 |  45689 45689 457 |    2  14   3 |
|    5   3   46 |     46    12  12 |    8   9   7 |
+---------------+------------------+--------------+

Very interesting and you are correct. I'd dub this a type 2b version of a Hidden UR. It’s the same principle as Type 2 but the floor is across two boxes. I've tested it against my 27k of 2010 stock and it appears twice as often as the Type 1 and three times as often as Type 2. I've added a section to Hidden Unique Rectangles with credit.

Might be a day or so before I can update the solver online.