<IfModule mod_rewrite.c>
  Options +FollowSymlinks
  RewriteEngine On
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteCond %{REQUEST_FILENAME} !-f

  ErrorDocument 404 /?mod=404 
  RewriteRule ^post_([0-9]+)\.html$ ?mod=post&id=$1 
  RewriteRule ^([a-zA-Z0-9_-]+).html$ index.php?mod=$1
 </IfModule>