• We should also discuss the choice of strategies for developing approximations, rather than the technical details. One example in DFT is to calculate the kinetic energy from a non-interacting system with the same density as the interacting one. Another example is to use the intuitive concept of nearsightedness. These are very general ideas that can be found -maybe under different names -also in contexts other than DFT, but they have all been important for the success of DFT.