  We introduce the notion of a normal gallery, a gallery in which any
configuration of guards that visually covers the walls covers the entire
gallery. We show that any star gallery is normal and any gallery with at most
two reflex corners is normal. A polynomial time algorithm is provided deciding
if, for a given polygon and a finite set of positions, there exists a
configuration of guards in some of these positions that visually covers the
walls but not the entire gallery.
