  A triplet $(\mathbb{P},\mathbb{F},S)$ of a probability measure $\mathbb{P}$,
of an information flow $\mathbb{F}=(\mathcal{F}_t)_{t\in\mathbb{R}_+}$, and of
an $\mathbb{F}$ adapted asset process $S$, is a financial market model, only if
it is viable. In this paper we are concerned with the preservation of the
market viability, when the information flow $\mathbb{F}$ is replaced by a
bigger one $\mathbb{G}=(\mathcal{G}_t)_{t\geq 0}$ with
$\mathcal{G}_t\supset\mathcal{F}_t$. Under the assumption of martingale
representation property in $(\mathbb{P},\mathbb{F})$, we prove a necessary and
sufficient condition for all viable market in $\mathbb{F}$ to remain viable in
$\mathbb{G}$.
