Before revision:  Two classical results drive the entire theory: the Kolmogorov-Cram\'{e The paper develops necessary and sufficient conditions for existence and uniqueness of particular and generic systems . The space of all solutions is characterized as an affine space in the frequency domain , which sheds light on the variety of solution methods considered in the literature .
After revision:  Two classical results drive the entire theory: the Kolmogorov-Cram\'{e The paper develops necessary and sufficient conditions for existence and uniqueness of particular and generic systems and characterizes the space of all solutions is characterized as an affine space in the frequency domain , which sheds light on the variety of solution methods considered in the literature .