Frobenius-Schur Indicators, the Klein-bottle Amplitude, and the   Principle of Orbifold Covariance
  The "orbifold covariance principle", or OCP for short, is presented to support a conjecture of Pradisi, Sagnotti and Stanev on the expression of the Klein- bottle amplitude. 
P. Bantay (Rolland Eotvos University, Budapest)