  It has recently been suggested \cite{Radicchi2013} that in a two-level
multiplex network, a gradual change in the value of the "interlayer" strength
$p$ can provoke an abrupt structural transition. The critical point $p^*$ at
which this happens is system-dependent. In this article, we show in a similar
way as in \cite{Garrahan2014} that this is a consequence of the graph Laplacian
formalism used in \cite{Radicchi2013}. We calculate the evolution of $p^{*}$ as
a function of system size for ER and RR networks. We investigate the behavior
of structural measures and dynamical processes of a two-level system as a
function of $p$, by Monte-Carlo simulations, for simple particle diffusion and
for reaction-diffusion systems. We find that as $p$ increases there is a smooth
transition from two separate networks to a single one. We cannot find any
abrupt change in static or dynamic behavior of the underlying system.
