@Netweb, thanks I got it.
Now I want to make a reverse function like I want to display all freshest topics except the one I displayed before.
So I am doing something like:
$left['show_stickies']=false;
$left['order']='DESC';
$left['post_parent']!=1263;
and then
if ( bbp_has_topics($left) )
bbp_get_template_part( 'bbpress/loop', 'topics' );
but its listing all of the topics.
When I go like $left['post_parent']=1263;
its ok, but when I want a negation (list all topics from all forums except the forum with 1263 ID, then in var dump of $left['post_parent']!=1263;
I am getting NULL