Open strings, simple currents and fixed points
  Some applications of simple current techniques and fixed point resolution to theories of open strings are discussed. In addition to a brief review of work presented in two recent papers with L. Huiszoon and N. Sousa, some new results concerning uniqueness of crosscap coefficients are presented, as well as a strange sum rule for the modular matrix implied by the existence of crosscaps. 
A.N. Schellekens