Computational Logic van Oystaeyen we introduce a new rock 9783642357213 we introduce a new rock cycling model of the continental crust and the concept of Geochemical Fields of Elements It focused on the genetic mechanisms underlying het erogeneity of tumor cell populations and tumor cell differentiation The work of COMPULOG acts as a focal point in this symposium which is broadened to cover the work of other eminent researchers in the field all ESPRIT Basic Research Actions have completed their first year and it is most encouraging and stimulating to see the flow of results such as the fine examples presented in this symposium