So, this has been done to a certain extent in variants (and it may have been done exactly, but I haven't heard of it)

Take a 19x19 board, overlay a transparency on top of it, create new boundaries with a marker, representing rivers, castles, whatever...

They're simply new edges of the board. Other than that the rules are the same. While it would be neat to have regions where stones have less liberties (and I know THAT has been done), I feel like it's exceptionally difficult for people to conceptualize the behavior when it stops being a grid, but I think new boundaries is something we could work with.

An example would be to play go on a stratego board, with those 3 bridges in the center, controlling them is important, since it can connect your power on one side, but at the same time, it's worthless if all you control are the bridges.

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Tactics yes, Tact no...

Perhaps a low-level proverb for such boards?: Convex corners, sides, concave corners, center (of course there are also alleys, bridges, and more complicated areas too)

One of the recent servers that was announced had that kind of Go: http://warlordgo.co.nr/

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a1h1 [1d]: You just need to curse the gods and defend.
Good Go = Shape.
Associação Portuguesa de Go

I'm not sure, but it could appear in the near future (if it didn't appear already). I'm sure most people up to 10k has thought of it at least once.
I was thinking that if all the hoshis were all dropped, then there would be more diagonal approaches.
The game play would be slightly different, but I would bet that Yi Setol would be #1 at that.

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LoL forum:
"Complexity is Magic: The Gathering, lots of tiny rules and special cases, and basically every single card is a unique case. Depth is Go: the game has 4 rules, and it takes literally decades to learn how to play that game well."

I once tried designng a board with a hole in it - a square concentrically inside a square. It quickly became obvious that with all that extra side to cower against, influence meant next to nothing, even with a 3x3 hole in the middle. The center of the board - 'center' in the influence vs territory sense - was a narrow ring, comprising less than 10% of the board. Everything else was an edge. A game would be a relatively simplistic race to get territory along the edges.

So in an attempt to redress that balance, I adjusted the numbers. The restrictions that I was trying to meet were these:
1) The board must be square, and an odd number.
2) The hole must be a square, and an odd number of 5 or larger. ( a 1x1 hole is uninteresting in that it has virtually no edge, and only corners. A 3x3 is little better )
3) The territory above the 4th rank must be close to 0.9 times the total territory below the 3rd rank. ( In a 19x19 board, the total territory under the 3rd rank is 17 * 2 * 4 = 136. The total territory above the 4th rank is 11 * 11 = 121. 121/136 =~ 0.9 ) Note that there are 8 third ranks and 8 fourth ranks instead of the usual 4.

A board 35X35 with a hole 7x7 was the smallest one that I could come up with.

This may not be best for I have no idea how to quantify the difference between a convex corner and a concave corner. There is a factor to convert one to the other. I know its sign but not its magnitude. I suspect for a 7x7 hole, a 31x31 board will be best, but that is just a hunch.

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Help make L19 more organized. Make an index: https://lifein19x19.com/viewtopic.php?f=14&t=5207

At the local club I tried this using square beer coasters.

Putting anything in the center makes for a rather boring game because the balance of power and territory will be gone.
But then I tried putting one in each of the four corners. this works quite well and gives a fun game.
It removes something like a 5x5 part of each corner, creating a total of 8 corners on the board.

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Laurens
Go school: freegame's Teaching School
Author of: The Next Move a book for 15-3kyu players.