  In the present paper, we study basic properties of digital n-dimensional
manifolds and digital simply connected spaces. An important property of a
digital n-manifold is that M is a digital n-sphere if and only if for any point
v of M, M-v is a digital n-disk. It is proved that a digital (n-1)-sphere S
contained a digital n-sphere M is a separating space of M. We show that a
digital n-manifold can be converted to the compressed form by sequential
contractions of simple pairs of adjacent points. We study structural features
of digital simply connected spaces. In particular, a digital (n-1)-sphere S in
a digital simply connected n-manifold M is a separating space of M.
