dailysudoku.com

[immpy]

Enjoy the puzzle.....

[Ajò Dimonios]

Hi everyone
One step solution after basics.

[Ajò Dimonios]

Hi everyone
Another one step solution after basics.

[JC Van Hay]

15 singles; r19c2.r9c3=28; 4 singles
The solutions of the 4s exclude {4r2c78, 4r7c7}
... Interpretation : X-Loop{4R19C9}
The solutions of the 7s exclude {7r1c7, 7r2c38, 7r3c5, 7r8c2}
... Interpretation : Pointings{7B45}, X-Chain{7C14B9}

The solutions of {(45)r6c7, (57)r7c7, (74)r9c8} exclude {4r45c8}; stte
... Interpretation : XY-Wing

[Ajò Dimonios]

Hi everyone
Another one step solution after basics.

[immpy]

Here, as promised from my previous puzzle posting, is the case where a Unique Rectangle will not work, because it occurs in four boxes, instead of two.
Notice the 47 in rows 1 and 9, columns 1 and 8. There is an extra candidate (8) in r1c8. If this were a true UR the 8 could be placed in this slot, but because the UR occurs (in this instance) in four boxes, it results in a contradiction. This means that the 8 cannot occur in r1c8.
Once that 8 is eliminated, the puzzle quickly solves with basics from there.

The first time I ran into this (in a previous puzzle long ago) I was dumbfounded when the usually reliable UR resulted in a contradiction. And the underlying reason was the occurrence of the UR in four boxes, as opposed to two. Chalked it up to another learning experience when it comes to Sudoku solving.

Hoping this example enlightens others.

immpy

[Ajò Dimonios]

Hi Immpy

Immpy wrote:

[immpy]

Indeed yes, Paolo, your reasoning is spot-on and that is the correct way of applying the Non UR technique. It all ended up the same in this case, but I shall be more mindful of this in the future.
But I just have to ask....if the 8 cannot go there, why not just eliminate it as a candidate?

Thank you Paolo....

immpy

[Ajò Dimonios]

Hi Immpy

Immpy. The fact that in this case UR technique can not be applied, because the vertices of the unique rectangle are placed on four boxes, it does not make any decision on candidate 8 positioned in the R1C8 cell. This means that it may be true or false. To be eliminated, it is necessary to demonstrate falsehood by applying a logic technique. Only using the trials and errors technique together with an x-wing can prove the false of 8 in R1C8.


p.s. I do not know the Non Unique rectangle technique.

Ciao a Tutti

Paolo

[immpy]

The Non Unique Rectangle is not really a technique that one could or should know, it is just the name I gave to it because it is NOT a Unique Rectangle (because of the four box occurrence).

Totally agree with you on the logic sequencing for this instance.

My next posted puzzle will bring up something even more baffling (at least for me, anyway).

Stay tuned.....


Thank you Paolo...

immpy

[immpy]

Please disregard my comment concerning my next posted puzzle. I discovered why I was baffled; the puzzle had multiple solutions so I scrapped it.

But I HAVE posted a new puzzle, which is legit.

Thanks all,

immpy