  We study the inverse problem for the Hankel operators in the general case.
Following the work of G\'erard--Grellier, the spectral data is obtained from
the pair of Hankel operators $\Gamma$ and $\Gamma S$, where $S$ is the shift
operator.
  The theory of complex symmetric operators provides a convenient language for
the description of the spectral data. We introduce the abstract spectral data
for the general case, and use the dynamical system approach, to reduce the
problem to asymptotic stability of some contraction, constructed from the
spectral data.
  The asymptotic stability is usually the hard part of the problem, but in the
investigated earlier by G\'erard--Grellier case of compact operators we get it
almost for free.
  For the case of compact operators we get a concrete representation of the
abstract spectral data as two intertwining sequences of singular values, and
two sequences of finitely supported probability measures. This representation
is different from one treated by G\'erard--Grellier, and we provide the
translation from one language to the other; theory of Clark measures is
instrumental there.
