2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/67274Gross and Zagier proved a formula for the absolute norm N(j(α_1) - j(α_2)) of a difference of singular values of the modular function j. We formulate and prove the analogues of their result for a number of functions of level 2 and 3.This paper is part of my thesis 'Primitive roots and singular moduli'Number Theorytext