You're right that retrieval practice isn't optimal for all types of knowledge. But not all spaced repetition systems are flashcard systems. Just under a month

You're right that retrieval practice isn't optimal for all types of knowledge. But not all spaced repetition systems are flashcard systems. Just under a month ago, I read about 'math academy' here on HN. One thing it does is sort of what it sounds like you envisage: surfacing exercises relating to concepts you might be about to forget.