To memorize text verbatim, you might find value in learning GMS. Mattias Ribbing has a course (search on coursio.io for his name) called "First Steps to a Complete Master Memory" and a follow-up course. This course is like the abridged version of GMS. To summarize in one sentence: GMS has you make palaces/journeys constructed from objects and their parts and you attach mnemonics to the parts. It is effective, but requires a decent amount of training. There is a second course called Pmemory (phenomenal memory) that has disappeared from the internet except for certain torrent websites. GMS (via Pmemory) was brought to the English-speaking world by an "interesting" character, but it was not invented by this character. I would suggest digging into the Pmemory material if you are serious, even though it can be a little confusing and overly prescriptive. But yes, I was able to memorize theorems and mathematical formulae verbatim. The time/energy cost was too high to maintain in my schedule, but I look forward to returning to the system in the future.