(in beta)
Invading large territories and defending against invasions is a very important part of go. Traditionally, these situations have been next to impossible to put into go problems because the branches are almost infinite. To solve this, we have a new class of problems, called Invasion Problems.
Your goal here is to invade a moyo successfully, living and reducing the enemy's points enough that you maintain a winning position.
The problem will end when the result has been decided: the invasion is clearly alive or dead, and the reduction is set. (There's some nuance here, and we may not always get it right. Please report situations that could be improved.)
When starting an invasion problem, you get to choose a difficulty level. This will determine the strength of your opponent. Note that the response moves will be played by AI: specifically Katago emulating a human at the given level. When you play a move, it will typically take a few seconds to get a response, as the computer thinks about it. (However, we are building up a database of responses, and so sometimes it may be fast.)
At the end of the problem, the board will mark what stones it considers alive and what are dead from your invading stones. The alive stones get a little green +, dead stones get a red X. If the state is indeterminate, it gets a triangle.
The user interface will try to explain a little bit about what happened. For example:
Or:
After completing a problem, you have the option to hit a research button which lets you explore more information about the problem and the result you reached.