  For separable metrizable spaces $X,Y$ and a metrizable topological group $Z$
by $S(X\times Y,Z)$ we denote the space of all separately continuous functions
$f:X\times Y\to Z$ endowed with the topology of layer-wise uniform convergence,
generated by the subbase consisting of the sets $[K_X\times K_Y,U]=\{f\in
S(X\times Y,Z):f(K_X\times K_Y)\subset U\}$, where $U$ is an open subset of $Z$
and $K_X\subset X$, $K_Y\subset Y$ are compact sets one of which is a
singleton. We prove that every separately continuous function $f:X\times Y\to
Z$ with zero-dimensional image $f(X\times Y)$ is a limit of a sequence of
jointly continuous functions in the topology of layer-wise uniform convergence.
