RewriteRule: redirect to index.php when not matching

Hi Everyone,
What I want to do is quite simple, but I don't know how to achieve it. And I have spend too many hours thinking about it.

This's the problem. My .htaccess file is as follows:

Options +FollowSymlinks
RewriteEngine on
RewriteRule ^.*login/?$ login.php
RewriteRule ^.*comment/?$ comment.php
RewriteRule ^.*blah/?$ blah.php

This allows me to redirect to the appropiate php file. For example, when the user enters the following url:
mycustomdomain.com/section1/section2/section3/../login

Apache redirects to the login.php file, no matter "section1/section2/section3/.." is.

What I want to do is redirect to index.php when my request doesn't match any of the above rules. For example, when the user enters the following url:

mycustomdomain.com/section1/section2/section3/../tralariquetevi

I would like to redirect the request to index.php, because "tralariquetevi" is not listed in the above rules.

How could I achieve that?
Thank you very much.

 

This is what I did, just in case someone has the same problem as me:

.haccess file:
--------------

# Rewrite mapping rules
RewriteRule ^(([^/]+/)*)login/$ login.php?path=$1 [L]
RewriteRule ^(([^/]+/)*)comment/$ comment.php?path=$1 [L]
RewriteRule ^(([^/]+/)*)page1/$ page1.php?path=$1 [L]
RewriteRule ^(([^/]+/)*)page2/$ page2.php?path=$1 [L]
RewriteRule ^(([^/]+/)*)page3/$ page3.php?path=$1 [L]

# Rewrite all requests to index.php
# except directories and files
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule . index.php [L]

Code (markup):

index.php file:
---------------

/* 
 * If '/' is missing at the end of the url request and it has no parameters, 
 * add it and redirect. 
 */ 
$info = parse_url($_SERVER["REQUEST_URI"]); 
$path = $info["path"]; 
if (!array_key_exists("query", $info) && !preg_match("#/$#", $info["path"])) { 
        header("Location: $path/"); 
        die(); 
}
// rest of code...

PHP:

page.php file:
--------------

/* 
 * If the request is not a valid url, print a 404 error 
 */ 
$path = array_key_exists("path", $_REQUEST)? $_REQUEST["path"]: NULL; 
if (!is_valid_path($path)) { 
        header('HTTP/1.0 404 Not Found'); 
        echo file_get_contents("templates/page_not_found.html"); 
        die(); 
}

PHP: