2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/64801This is the writeup of an expository talk. It is intended as an introduction to the work of Hopkins, Kuhn, and Ravenel on generalized group characters, which seems to fit very well with the theory of what physicists call higher twisted sectors in the theory of orbifolds.Talk at the ChengDu (Sichuan) ICM satellite conference on orbifolds, August 2002; Revised, with some confusion about homotopy quotients eliminated. To appear in the Proceedings of a conference on spin curves and Gromov-Witten invariants, ed A. Vaintrob et al, to appear in Contemporary MathAlgebraic TopologyMathematical Physics19Lxx, 55Nxx, 57Rxxtext