  It is widely believed that the stationary properties after a quantum quench
in integrable systems can be described by a generalized Gibbs ensemble (GGE),
even if all the analytical evidence is based on free theories in which the pre-
and post-quench modes are linearly related. In contrast, we consider the
experimentally relevant quench of the one-dimensional Bose gas from zero to
infinite interaction, in which the relation between modes is nonlinear, and
consequently Wick's theorem does not hold. We provide exact analytical results
for the time evolution of the dynamical density-density correlation function at
any time after the quench and we prove that its stationary value is described
by a GGE in which Wick's theorem is restored.
