Toward the M(F)--Theory Embedding of Realistic Free-Fermion Models
  We construct a Landau-Ginzburg model with the same data and symmetries as a $Z_2\times Z_2$ orbifold that corresponds to a class of realistic free-fermion models. Within the class of interest, we show that this orbifolding connects between different $Z_2\times Z_2$ orbifold models and commutes with the mirror symmetry. Our work suggests that duality symmetries previously discussed in the context of specific $M$ and $F$ theory compactifications may be extended to the special $Z_2\times Z_2$ orbifold that characterizes realistic free-fermion models. 
Per Berglund, John Ellis, Alon E. Faraggi, D.V. Nanopoulos and Zongan   Qiu