Proof That The Identity Function is Continuous if and only if the Destination Topology is Finer Than The Source Topology
Theorem
The identity functionis continuous if and only if
where
Proof
Suppose thatis continuous then
But hence
Now suppose thatis the identity function so that
and suppose
Let A in T_1 thenbecause T_1 in T hence f is continuous.
This theorem may be applied recursively so that if f,g,h are identity functions