  We present high angular resolution interferometric observations of the dust
continuum at 2.7 and 1.3 mm, and of the HC3N (12-11) and C18O (2-1) emission
around L1157-mm, a Class~0 object that drives a spectacular molecular outflow.
The millimeter dust emission is clearly resolved into two components, a
flattened compact source of ~450 x 250 AU at 1.3 mm, and mass ~0.1 Msun, plus
an extended envelope of ~3000 AU at 1.3 mm, and mass ~1.1 Msun. The millimeter
spectral index varies throughout the region, with the lower value found toward
the compact protostar, possibly indicating grain growth in the denser regions.
A strong interaction between the molecular outflow and the close protostellar
environment is taking place and affects the structure of the innermost parts of
the envelope. This is shown by the spatial coincidence between the molecular
outflow and the dust (1.3 mm continuum) and HC3N emission: both tracers show
structures associated to the edges of the outflow lobes. Basically, the global
picture sketched for the Class 0 object L1157-mm by Gueth et al. (1997) is
supported. We find possible evidence of infall, but we do not detect any
velocity gradient indicative of a rotating circumstellar disk.
