This is kind of similar to (1), but the main difference is that you removed all the burden of learning from the spaced repetition process. This allows you to kind of backtrack and say to yourself, “what is an example of something that, if I forgot how to do, I would be regressing my knowledge”. This seems to enable some more free form types of spaced repetition prompts, like every repetition is a new problem of a specific kind that I should be able to solve, and I have to solve it to make sure that I haven’t forgotten how to do it. This is a bit outside of the normal research done regarding spaced repetition, since forgetting how to solve a problem isn’t usually remedied simply by seeing the solution (though it could be!). Nonetheless, even this kind of “spaced practice” probably has a similar type of forgetting curve and could be optimized with the similar algorithms.