udosuk wrote:If your solver can't solve this one easily, then you should seriously consider teaching it some tricks on 90 symmetry.

Hi,

This question was still pending, waiting for implementation of 90° symmetry.

Here is the answer

- Code: Select all
`+-------+-------+-------+`

| . . . | . . 1 | . 2 . |

| 3 . . | . . . | 4 . . |

| . 4 2 | 5 . . | 6 . . |

+-------+-------+-------+

| 7 . . | . 6 . | 3 . . |

| . . . | 2 . 5 | . . . |

| . . 6 | . 3 . | . . 8 |

+-------+-------+-------+

| . . 3 | . . 2 | 5 4 . |

| . . 4 | . . . | . . 6 |

| . 5 . | 9 . . | . . . |

+-------+-------+-------+

r2c5=2 r5c2=3 r5c8=6 r8c5=5

r5c5=4 r1c4=4 r4c9=4 r6c1=4 r9c6=4

r1c1=5 r1c9=3 r2c6=6 r3c6=3 r4c2=2

r4c3=5 r6c7=2 r6c8=5 r7c4=6 r8c4=3

r9c1=6 r9c9=2 r1c2=6 r2c9=5 r8c1=2

r9c8=3

And the tagged (partially) map of candidates at this point.

The most important was for sure r5c5=4.

Nevertheless, the solver uses symmetry to produce these 2 AICs

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`5 6 7f89h |4 789 1 |7k89 2 3`

3 178d9 1789 |7A8a 2 6 |4 1789d 5

189k 4 2 |5 7e89 3 |6 1789 1f7h9

----------------------------------------------------

7 2 5 |1a8A 6 8a9A |3 1A9a 4

189 3 189e |2 4 5 |1e79 6 179

4 1a9A 6 |1A7a 3 7A9a |2 5 8

----------------------------------------------------

18h9f 1789 3 |6 178e 2 |5 4 1k79

2 1d789 4 |3 5 7a8A |1789 17d89 6

6 5 178k |9 178 4 |1h78f 3 2

[]9r1c3.h - 7r1c3.f = 7r2c23.F - 7r2c4.A = 1r6c2.a - 1r8c2.d = 1r8c78.D - 1r9c7.h

[]1r7c9.k - 1r89c7.E = 1r5c7.e - 1r5c13.A = 1r6c2.a - 1r8c2.d = 1r8c78.D - 1r7c9.k

candidates tagged 'h' or 'k' are eliminated

and one XYWing eg: r3c9 19 r1c7 89 r3c1 18

gives singles to the end

champagne

PS: what is missing in my sample file is an example of double diagonal symmetry. Can anybody fill the gap??