Manin–Drinfeld theorem
In mathematics, the Manin–Drinfeld theorem, proved by Manin (1972) and Drinfeld (1973), states that the difference of two cusps of a modular curve has finite order in the Jacobian variety. == References == Drinfeld, V. G. (1973), "Two theorems on modular curves", Akademija Nauk SSSR. Funkcionalnyi Analiz i ego Priloženija, 7 (2): 83–84, ISSN 0374-1990, MR 0318157 Manin, Ju.