dailysudoku.com

[dongrave]

I have another question about Eureka notation. Below is a grid that I arrived at after performing the basics of problem #513416 from 1sudoku.net (rated Evil).

[Marty R.]

Yes, it's generally accepted. Don't forget, AIC = Alternating inference chain, so the = and - represent strong and weak inferences, respectively.

In your "if then" example. I'd have probably started with (5-9)=9r9c2 In your notation line, I'd have written the 3rd term as (9=7). How about an example of that chain that doesn't alternate between strong and weak?

I rarely (if ever) see chains that don't alternate.

[dongrave]

[Marty R.]

Don, I didn't think about the inferences when reading the "if then". I'm not saying I'm doing the right thing, but I go ahead and notate without giving much thought to how the numbers fit the definitions of strong and weak.

To notate your "if then", it's necessary to use ALS's (almost locked sets), an incredibly powerful tool. In this case, we're using ALS's as a way of notating what we know is right by doing the steps in our heads. Eureka doesn't seem to lend itself well when the solution gets into locked sets. ALS's can be used creatively to alter (or affect) the solution. Here's my interpretation of the "if then" example.


if r7c1=5, then r9c2=9 so r9c6=4 so r8c4=7 so r4c4=9 so r4c1=5


(5-9)r7c1=r9c2-(9=74)r9c86-(4=197)b8p234-(7=9)r4c4=> -9r4c1

Note the 3rd term. The b8p234 is a way of identifying cells when there's an ALS confined to a box. The "p" stands for "point" and refers to the cells' position in the box, 1-9 going from left to right and down. It's much simpler and easier to follow than listing all the individual cells.

[dongrave]

Wow! Thanks Marty! That is interesting! (And not obvious!) I really appreciate your help! Don.