Classification and a toolbox for orientifold models
  We provide the general tadpole conditions for a class of supersymmetric orientifold models by studing the general properties of the elements included in the orientifold group. In this talk, we concentrate on orientifold models of the type $T^6/Z_M\times Z_N$. 
P. Anastasopoulos (Crete U, Ecole Polytechnique), A. B. Hammou (Crete   U, USTO)