i built a pdf reader for math textbooks because i kept losing my place

working through a stats textbook, i spent half my time flipping back to "see (3.41)". so i built lemma: it reads the pdf once and turns references into links you can preview, folds proofs, and checks the derivations you write. select a passage and it asks your favorite llm (chatgpt, claude, gemini) to explain it, cited equations included, and keeps the answer next to the passage. free and open source, mac only for now. if you read math-heavy pdfs on a mac, i'd like to know where it breaks: github.com/fus3r/lemma