Thanks for the suggestion. The app already has export and import functions, so it would be nice to have established notes. But I also think people need a note-taking and organizing something by themselves for learning. I think that's why people take notes even though they have well-organized tons of books.

I'm not really sure what it means for the forking mechanism. I would be grateful if you could show me a link to the resource for the forking mechanism you mentioned.

As for the tree structure, the tree structure is already reflected to some extent. As with breadth-first search, the questions starts from the higher level, but when the parent node is in the wrong state, the child node does not appear in the problem. I'll search more about the half-life regression you mentioned!