An ideal independent source as an equivalent 1-port
  We consider a 1-port, not necessarily linear, with a dependent source, appearing at the port. The control of the source is entirely internal for the 1-port. If this source is a parallel voltage source, then the equivalent circuit is an ideal independent voltage source, and if it is a series current source, then the equivalent circuit is an ideal independent current source. (As usual, "ideal" source is defined as a source whose proposed function is independent of the load.) In the simple LTI case, these results can be obtained, respectively, by either taking RTh zero in the Thevenin equivalent, or taking RN infinite in the Norton equivalent; however the very fact that the final circuits do not include any linear elements indicates the possibility of generalization to nonlinear 1-ports. Some limitations on the circuit's structure (functional dependencies in it) are required, and the clearness of these limitations, i.e. clearness of the conditions for the 1-port to be an ideal source for any load, is the aesthetical point. 
Emanuel Gluskin, Anatoly Patlakh
physics.gen-ph