TITLE: On non-smooth pitchfork bifurcations in invertible quasi-periodically forced 1-D maps AUTHORS: Angel Jorba^(1), Francisco Javier Mu\~noz-Almaraz^(2), Joan Carles Tatjer^(1) (1) Departament de Matematiques i Informatica Universitat de Barcelona, Gran Via 585, 08007 Barcelona, Spain (2) Universidad CEU-Cardenal Herrera, Departamento de Ciencias Fisicas, Matematicas y de la Computacion. Alfara de Patriarca, Valencia, Spain. E-mails: angel@maia.ub.es, malmaraz@uchceu.es, jcarles@maia.ub.es ABSTRACT: In this note we revisit an example introduced by T. Jager in which a Strange Non-chaotic Attractor seems to appear during a pitchfork bifurcation of invariant curves in a quasi-periodically forced 1-d map. In this example, it is remarkable that the map is invertible and, hence, the invariant curves are always reducible. In the first part of the paper we give a numerical description (based on a precise computation of invariant curves and Lyapunov exponents) of the phenomenon. The second part consists in a preliminary study of the phenomenon, in which we prove that an analytic self-symmetric invariant curve is persistent under perturbations.