On Derivation of Discrete Time Fourier Transform from Its Continuous Counterpart

This paper is devoted to some problems that appear in derivations of the discrete time Fourier transform from a formula for its continuous counterpart transformation into frequency domain as well those regarding inverse direction. In particular, latter ones remained so far an unresolved problem. It solved first here. Many detailed explanations accompanying solution found are presented. Finally, it also worth noting our do not exploit any such sophisticated mathematical tools so-called Dirac delta and comb.