Question: *This is a multipart Index question:*

1. Is there a way one can create index
on index?
2. Why would one wish to to so?
3. And if so, are there any examples?

Answer: 
**NO**, Indexes are meant for **COLUMNS IN TABLES**

[How MySQL Uses Indexes](http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html)

> 
> Indexes are used to find rows with
>  specific column values quickly.
>  Without an index, MySQL must begin
>  with the first row and then read
>  through the entire table to find the
>  relevant rows. The larger the table,
>  the more this costs. If the table has
>  an index for the columns in question,
>  MySQL can quickly determine the
>  position to seek to in the middle of
>  the data file without having to look
>  at all the data. If a table has 1,000
>  rows, this is at least 100 times
>  faster than reading sequentially.
> 
> 
>
You can see from syntax diagram for [create index](http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/statements_5010.htm) in the oracle documentation that it does not apply to indexes.  

Nor can I think of a reason you would want to.