udosuk wrote:Make sure you read this very thread carefully too, starting from p.1.

No problem, it is a ONE page thread

But it is an old one. Meantime, I red a very nice probe excluding "Unicity use".

I am not sure I covered all the field, but, regarding symmetry

. 90° rotationnal symmetry => 180° rotationnal symmetry.

. I do not foresee a possibility to have a=>b and b=>c in symmetries with fix cells if a,b,c are different.

In all identified cases a<=>b is compulsory.

. Mauricio gives an example of double diagonal symmetry, this is for me identical to 180° rotationnal symmetry. The findings shown rely on constraints of other given. Only the central assignement comes out of the symmetry property.

The door is still open for other examples, but I doubt.

In total, after the wise remark of eleven, 2 possibilities are still there for me:

.180° rotationnal symmetry => r5C5 center of the symmetry

.diagonal symmetry.

udosuk wrote:http://forum.enjoysudoku.com/viewtopic.php?t=6459

It might help a bit, but mind you, in that thread (Glyn's riddle) the situation is very different, as the puzzle on offer doesn't have symmetry in the strict sense, but we can just work out from Glyn's cryptic hints how some of the cell values in the solution grid display partial symmetry.

I came t the same conclusion after a new carefull reading. As a matter of fact, I lost interest in that thread.

udosuk wrote:champagne wrote:The most difficult is to recover the symmetry in a scrambled puzzle.

Well, it's certainly a skill that needs a lot of practice, and an exceptional observation power.

I never said I did not covered that topic. Not so difficult for a computer, just needing more code.

At the end, pending interesting question remain:

Have you other examples of symmetry not covered in the previous step (including morphing of the puzzle), and what are you doing out of them.

champagne