Two questions about Kramers-Kronig transformations

Using the Kramers-Kronig(KK)transforms, the real part of a transfer function can be calculated, for a causal, stable, linear, time invariant and finite system when f→0 and f→∞, when the change in its imaginary part, as a function of the frequency, is known. At the opposite, the imaginary part of a transfer function can be calculated when the evolution of its real part is known.