The nonlinear-by-switching systems (a heuristic discussion of some basic   singular systems)
  Electronics has changed greatly during recent decades, and some its basic concepts should be revisited. Starting from the sampling procedure, we consider some mathematical, physical and engineering aspects related to singular, mainly switching, systems. Since the field of such systems is very rich in content, a certain line of treatment had to be chosen, making the work a theoretical introduction to the field of the systems. The focus is on the conditions for a singular system to be linear or nonlinear, and one studies more deeply what "nonlinearity" is (can be). In order to uniformly present mathematical, physical and circuit arguments, the work is given the frame of a discussion in which the relevant specialists participate. 
Emanuel Gluskin