The computer system of claim 11, wherein I1 specifies an energy type E1 at each of said I/O locations on S1, wherein I2 specifies an energy type E2 at each of said I/O locations on S2, wherein L specifies an energy type E for each electrical net in L, and wherein a second necessary condition for the relationship between L and I to be mutually consistent is that the energy types in L and the energy