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[ZeroAssoluto]

Hi everyone,

[Earl]

If basics are used first, the 123xywing should do it.

Early Earl

[ZeroAssoluto]

If you don't delete number 3 from r3c3 (with the XY-Wing) you don't have the LC in column 2 with number 3.

Ciao Gianni

[TomC]

Or you could say a=4 to solve

[Mogulmeister]

Picking up a little on all these themes there is another structure that gets us to the same conclusion as Tom’s contradiction.

Using Tom’s grid, incorporating a, is an ANP <139> at r12c2.

If ANP is true then the <13> pair eliminates the <3> at a making a = 4

If ANP is false then r2c2 = 9 which creates an XY wing with c and d.
This makes b = 3 and this makes a = 4.

[Mogulmeister]

[TomC]

I think it's always good to look at solutions in different ways.

The ANP by Mogulmeister could also be looked at as:

In box 1 it doesn't matter where you put <9> "a" is always <4>

[Mogulmeister]

That’s right. Thanks Tom. Should have made that explicit. Whether ANP true or false or wherever the 9, the answer is that “a” is always 4

[ZeroAssoluto]

[Mogulmeister]

I think the basic must come after the <123> ?
Once you have removed the 3 from r3c3 it is just basics.

[ZeroAssoluto]

When I talk about basics I am talking about the simplest techniques (LC, Pairs, Triples).

In this case I think LC should come after XY-Wing, not before, not as the first step.

[Mogulmeister]

Yes that is also what I was saying. I think Earl may have meant to say xy wing and then “btte.” I think we note basics but don’t regard them as a step as the eliminations are implicit.