Theorem
Let
be the set of all loops in
with base point
The relation 'homotopic relative to
labelled by
defined on
is an equivalence relation.
Proof
since we can define
such that
for all![]()
since if
there exists a continuous functio
such that
so define
then
and
so![]()
is continuous since
is.
If
there exists
such that
if
there exists
such that![]()
Define
Then
and
and
is continuous hence![]()