Conditional redirection for SSI in vbscript

I am making a website using server side includes. I have a doubt.
I have 4 pages:
index.asp
head_ssi.asp
body_ssi.asp
foot_ssi.asp

head_ssi.asp, body_ssi.asp & foot_ssi.asp are server side includes of index.asp.

Now i want set it in such a way that if “head_ssi.asp” is tried to access to directly, it should be redirected to “index.asp”