In this section the ``common'' models are described. Since the ``popular'' model also known as Garber's model never work (even by its own creator)4, several other models have appeared. These models are described here to have a clearer picture of what was in the pre Bar-Meir's model. First, a description of Garber's model is given later Brevick's two models along with Miller's model5 are described briefly. Lastly, the EKK's numerical model is described.