u/Helpful-Fuel-7568

Friends! I think after a couple weeks of practicing Im confident I can solve finned swordfishes, theres one thing I cant understand:

Why is R8C9 assumed to be the fin?? As opposed to R4C7? (Both circled) Neither cells share a column.

IN ADDITION! How can R8C9 be a “FIN”? Making it a fin makes the swordfish incomplete? I cant wrap my head around the geometry.

You can run a true/ false chain starting at either end of the fins and eliminate the candidates that both fins see, this is really an X-Chain

Is this a finned X-Wing if so can I delete r3c7?

Neither G6 nor E4 see a column so why is G6 choosen as the fin and not E4?

Correct me if Im wrong but the eliminations only work when G6 is part of the fish. When E4 is false either G7 or i7 could be 5

In the fish they temporarily deleted 5 from i2 to solve the fish then later In the solution they claim that i2 must be 5, how is that a possibility when we solved the fish with the assumption that i2 was NOT 5?? 🤨 Shouldnt i2 be deleted??

1st pic - Finned swordfish (does a unfinned swordfish exist?, such that is a “plain” swordfish?)

2nd pic - Is this supposed to a disguised x-chain?

3rd pic - where the hell did the get the cahoots to arbitrarily ASSUME that R8C9 isnt a 1?? Why couldnt R8C6 be choosen? It looks like it has something to do with matching columns

4th pic - The claim is that D7 MUST be 1?? How the heck is that determined??? By running a chain starting with R8C6 being true? If so if R8C6 is false then D7 (R4C7) would be false as well.

5th pic- I understand what to delete except non of the steps for why its deleted.

If the two main questions 1.) How or why do we assume R8C9 (H9) is not 1? 2.) Is this a chain starting with R8C6?

Ive got many more of these examples by the way 😅😅😅

Please halp,

Confused dummy

*bonus question- why couldnt row 5 or 7 be used instead of row 8?

Hello guys, I was told all skyscapers are X-Chains but not all X-Chains are skyscrapers. So, with that being said assuming R1C7 is true, then R1C5 is false, then R9C5 is True and R9C8 is false.

If R9C8 is false how does that make R2C8 false?? There is no bi-value or bi-local relationship between 6s in column 8?

I guess i understand that if R1C7 is true then there can be no more 6s in box 3. But that seems to imply that R1C7 must be true while its only an assumption. I think that my only caveat

Rows: Letters
Columns: Numbers

Hallo, its me again. Just when I thought I understood W-Wings another doozie comes along and blows me out the water.

When G9 is 3 it kills the 3s in row G. When E4 is 3 it kills the 3s is column 4. This contradicts or violates box 8 because that would leave no spaces for 3 (poor guy).

According to SudokuCoach, I should be able to eliminate the 1 from the conjugate cell E9………

BUT……….

Thats not what the app tells me to do. It says to Eliminates the 3s that i7 and e4 see.

I dont understand where the logic comes in to delete 3 from e7 and i4.

I have failed

Can someone, anyone, please explain why the digit 2 is the focal point when the pair is (2,5) How do we determine that 2 in the pivot digit? Is it because 2 is bi-value and bi-local in Row 6 and Column 4?

Two things!

1.) The hint says is if F3 is 2 then D2 is 5, and if F4 is 2 then C4 is 5. However F3 and F4 cannot both be 2 at the same time! Since they both cant be 2 at the same time then how ca we conclude that D2 and C4 must be 5, because theyre only 5 if F3 and F4 are both 2. So that logic is invalid yes?

2.) Next, even if I take point 1 at face value, i thought W-wings force contradictions? How does eliminating C2 prevent an invalid row, column or box?

Please help.

Sincerely,

Confused guy

I need help please. SudokuCoach explains how to identify and solve W-wings in a way that Ive never seen come up in the field.

SudokuCoach says to identify two bi-value cells that dont see each other, find a connecting cell and force contradictions. In there example if the 1 is true, then both 7s must be true, however that cant be true because leaves no available spaces for 7 in box 6. That part is crystal.

However in my app I have 3 examples Ive come across where thats the case for none of them.

In the example above from my app (pics 5-7), there is no cell where a digit forces an invalid box. Instead it took a full day in between work to try and reason through the logic.

Basically the app’s hint implies (in every case so far) to identify 3-4 bi-value cells which must also be bi-local. Identify a pivot cell which sees both bi-value cells. Then reason through which digits can be eliminated.

If anyone is able to explain, why in the app’s example there is no forced contradiction like in the sudokucoach example?

Confession: I use fast pencil! 😆 Sometimes “expert” is easier than the easy puzzles 😅

Eliminating 6s

Yellow - Base

Green - Walls

Red - Tops

Something is fundamentally wrong with my understanding of skyscrapers. Why cant I eliminate R8C8????

I cant eliminate anything in box 4 (boxes counting from left to right) because the top of the skyscraper is in box 7.

But why cant I eliminate the 6 in box 9. The left side top of the skyscraper sees box 9 and is also in the same column.

The craziest part is played an extreme puzzle yesterday with 8 similar skyscrapers and I eliminated every number based on this (seemingly wrong logic).

Please halp, I have the dumb.

At my wits end as per usual, went over this map 3 times until I got cross eyed plus with a bonus headache this time. I had to give in and use a hint that I dont know how to use. Im at least 6 months away before I can learn a swordfish. Do you guys see any other hints available?

*Sidenote: All of this to eliminate one 5, reminds me of my stats class where I spent 30 minutes working on 1 problem only to find out the answer was 2.903

Is this a valid X- Wing and if so are these the only eliminations? Wondering if I can kill R3C7

The red circled cell (4,5) in R4C3. At this point Doesnt matter what number the cell is all the that matters is that it forces each of the circled GREEN cells to be a 1.

When its 5 it forces green circled R6C2 to be 1 (eliminating the 1s in the column).

When its 4 it forces green circle R1C3 to be 1 (eliminating the 1s in the box).

Hence it doesnt matter if the red circled cell is 4 or 5, or which green circled cell is 1, any combination of all those possibilities forces those 1s (that are x’d out) to be eliminated.

This is sort of like a backwards logical deduction where you start at the end first. Very new way of thinking for me, thought I’d share.