  Two-phase solutions of focusing NLS equation are classically constructed out
of an appropriate Riemann surface of genus two, and expressed in terms of the
corresponding theta-function. We show here that in a certain limiting regime
such solutions reduce to some elementary ones called "Solitons on unstable
condensate". This degeneration turns out to be conveniently studied by means of
basic tools from the theory of Riemann-Hilbert problems. In particular no
acquaintance with Riemann surfaces and theta-function is required for such
analysis.
