Life In 19x19http://lifein19x19.com/ [Hactar Go] Why is this tsumego solution correct?http://lifein19x19.com/viewtopic.php?f=11&t=17305 Page 1 of 1

 Author: libcat [ Thu Mar 05, 2020 12:42 pm ] Post subject: [Hactar Go] Why is this tsumego solution correct? -Edit - I got a bit confused with my diagrams in my first post so this is the correction version. I have just started learning using the Interactive Way to Go website (it's so good!) and solve Tsumego on my phone, but the app I use doesn't really explain why a certain shape is the correct solution. Here is the problem from the Hactar Go Lite phone app. White to play. Click Here To Show Diagram Code`[go]\$\$Wc\$\$ +-------------------+\$\$ | O X . O . . . . . \$\$ | O X X X X X X X O \$\$ | O O O O O O O O . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ +-------------------+[/go]`I finally arrive at the solution: Click Here To Show Diagram Code`[go]\$\$Wc\$\$ +-------------------+\$\$ | O X . O 3 . 2 1 4 \$\$ | O X X X X X X X O \$\$ | O O O O O O O O 5 \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ +-------------------+[/go]`I'm guessing that White needs to stop Black from forming two eyes and living. So why is the above correct? Because I can see that Black has two eyes, one big one of the left and a small one on the right. Maybe I have completely misunderstood the point of this tsumego or the concept of forming eyes. Assuming that Black wants to form two eyes, could it then play either a or b? It looks okay to me. Click Here To Show Diagram Code`[go]\$\$Wc\$\$ +-------------------+\$\$ | O X a O 3 b 2 1 4 \$\$ | O X X X X X X X O \$\$ | O O O O O O O O 5 \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ | . . . . . . . . . \$\$ +-------------------+[/go]`

 Author: EdLee [ Thu Mar 05, 2020 4:03 pm ] Post subject: Hi Libcat,B has only one real eye, and is dead.(a) and (b) are two liberties, not two eyes.(c) is a False Eye. Click Here To Show Diagram Code`[go]\$\$B Black Dead shape\$\$ +--------------------\$\$ | a O O b X c X . . .\$\$ | X X X X X X O W . .\$\$ | O O O O O O . . O .\$\$ | . . . . . . . . . .[/go]` Click Here To Show Diagram Code`[go]\$\$W Black Dead shape\$\$ +---------------------\$\$ | . O O . X 2 X 1 . .\$\$ | X X X X X X O O . .\$\$ | O O O O O O . . O .\$\$ | . . . . . . . . . .[/go]`As an exercise, try to prove to your satisfaction that B cannot form two real eyes with this shape: Click Here To Show Diagram Code`[go]\$\$B Black Dead shape\$\$ +--------------------\$\$ | . O O . X X X O . .\$\$ | X X X X X X O O . .\$\$ | O O O O O O . . O .\$\$ | . . . . . . . . . .[/go]`Did you mean to make 9x9 boards in your diagrams ?... because your diagrams are open-ended on the right edge.If your diagrams are supposed to be 9x9, then in your second diagram,your at J7, in reply to J9, is correct.In the diagrams here, I made the boards bigger than 9x9,and in reply to , W extends toward the right with .

 Author: Kirby [ Thu Mar 05, 2020 5:06 pm ] Post subject: Re: [Hactar Go] Why is this tsumego solution correct? The problem makes sense now, with the better diagrams. I removed your other thread, since it was confusing.

 Author: libcat [ Fri Mar 06, 2020 8:48 am ] Post subject: Re: @EdLee Hello and thank you!EdLee wrote:Did you mean to make 9x9 boards in your diagrams ?... because your diagrams are open-ended on the right edge.If your diagrams are supposed to be 9x9, then in your second diagram,your at J7, in reply to J9, is correct.In the diagrams here, I made the boards bigger than 9x9,and in reply to , W extends toward the right with .Yes, I did not even realise this until checked my phone again. Here is the screenshot. It looks like everything was supposed to be happening on the top right of a 19x19 board, so technically yes, 9x9. I hadn't thought about this up till now, but clearly where the tsumego takes place/board size makes a huge difference! Sorry for missing that big detail.I will have to check my understanding of all the concepts you linked to - especially false eyes since they don't look appear obvious to me. EdLee wrote:As an exercise, try to prove to your satisfaction that B cannot form two real eyes with this shape: Click Here To Show Diagram Code`[go]\$\$B Black Dead shape\$\$ +--------------------\$\$ | . O O . X X X O . .\$\$ | X X X X X X O O . .\$\$ | O O O O O O . . O .\$\$ | . . . . . . . . . .[/go]` ARGH okay yes, I see. Thanks again.

 Author: libcat [ Fri Mar 06, 2020 9:21 am ] Post subject: Re: [Hactar Go] Why is this tsumego solution correct? Kirby wrote:The problem makes sense now, with the better diagrams. I removed your other thread, since it was confusing.Thank you! (I don't know what the etiquette is here i.e, do I 'like' your reply? No idea, but either way I'm grateful)

 Author: Joaz Banbeck [ Thu Aug 27, 2020 10:47 am ] Post subject: Re: Re: libcat wrote:... false eyes since they don't appear obvious to me. The easiest way to understand a false eye is to ask yourself how it will eventually resolve. ( Works for lots of other shapes too, FWIW )If you look at the example used above... Click Here To Show Diagram Code`[go]\$\$B False eye\$\$ +--------------------\$\$ | . O O . X C B O . .\$\$ | X X X X X X O O . .\$\$ | O O O O O O . . O .\$\$ | . . . . . . . . . .[/go]`you can realize that,sooner or later, ONE player must play BOTH of the circled points.In other words, this: Click Here To Show Diagram Code`[go]\$\$B Not in this universe\$\$ +--------------------\$\$ | . O O . X B W O . .\$\$ | X X X X X X O O . .\$\$ | O O O O O O . . O .\$\$ | . . . . . . . . . .[/go]`...sharing of the two points cannot ever exist. Try it on a board to prove it to yourself.Even if both players cooperate, you can't get there from here.So, eventually it must end like this: Click Here To Show Diagram Code`[go]\$\$B Dead with one eye\$\$ +--------------------\$\$ | . O O . X B B O . .\$\$ | X X X X X X O O . .\$\$ | O O O O O O . . O .\$\$ | . . . . . . . . . .[/go]`...or this: Click Here To Show Diagram Code`[go]\$\$ Dead with one eye\$\$ +--------------------\$\$ | . O O . X W W O . .\$\$ | X X X X X X O O . .\$\$ | O O O O O O . . O .\$\$ | . . . . . . . . . .[/go]`BTW, I'm assuming in this post that you know basic dead/live shapes, and therefore you know that this: Click Here To Show Diagram Code`[go]\$\$B Basic dead shape\$\$ +--------------------\$\$ | . O O . X O .\$\$ | X X X X X O .\$\$ | O O O O O O . \$\$ | . . . . . . .[/go]`..is dead.

 Author: Joaz Banbeck [ Thu Aug 27, 2020 11:30 am ] Post subject: Re: [Hactar Go] Why is this tsumego solution correct? This is not the first time that the issue has been discussed.For a slightly different statement of the issue, have a look at this: https://lifein19x19.com/viewtopic.php?f=11&t=16767

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