I think this is a useful idea, although I'm not sure how useful this particular example is. FWIW, I definitely remember this from revising maths proofs -- each proof had some number of non-obvious steps, and you needed to remember those. Sometimes there was just one, and once you had the first line right, even if there was a lot of work to do afterwards, it was always "simplifying in the obvious way", so the rest of proof was basically "work it out, don't memorise it". Other proofs had LOTS of non-obvious ideas and were a lot harder to remember even if they were short.