Let φ be a closed continuous
mapping from X onto Y. It is an open problem whether the realcompactness of X
implies the realcompactness of Y. Concerning this problem, in case φ is an open
WZ-mapping, we discuss the structure of the image space Y under φ and give a
necessary and sufficient condition that Y be realcompact. We also show
that if X is locally compact, countably paracompact, normal space then
the image space Y of X under a closed mapping is realcompact when X is
realcompact.