and
are topological spaces, the homology group
is not
necessarily isomorphic to the direct sum of
and
.
,
,
be Hausdorf, path-connected, locally
path-connected. Let
be maps, with
.
and
are covering space projections then
is too.
has a universal covering space, and if
,
are covering space projections, then
is too.
and every
a map
of degree
.
-manifold can be embedded in
Euclidean space of some dimension
.