In HTML, this is impossible. Going "back" means that you go
to the previous page in your history. You might be able to
create a link to the URL specified in the "HTTP_REFERER"
environment variable in your document, but that only creates
a link to a new location in your history. Even worse, the
information in that variable can be plain wrong. Some
browsers incorrectly send the variable when you use a
bookmark or type in an URL manually, and some don't send
that variable at all. Then you would end up with an empty link.

A JavaScript could use "history.back()" to do this, but this
only works in Netscape 2.