Someone

<IfModule mod_rewrite.c>
    RewriteEngine On

    RewriteBase /gallery2/

    RewriteCond %{REQUEST_FILENAME} -f [OR]
    RewriteCond %{REQUEST_FILENAME} -d [OR]
    RewriteCond %{REQUEST_FILENAME} gallery\_remote2\.php
    RewriteCond %{REQUEST_URI} !/gallery2/main\.php$
    RewriteRule .   -   [L]

    RewriteCond %{THE_REQUEST} /gallery2/a/*([^?]*)(\?.|\ .)
    RewriteCond %{REQUEST_URI} !/gallery2/main\.php$
    RewriteRule .   /gallery2/%1
</IfModule>