public function sub_cards($slug) {
	    $subvocab= Vocabulary::get( 'conversations' );
        $subcards= $subvocab->get_term($slug)->descendants();
        $slugs= array();
        foreach($subcards as $subcard) {
            $slugs[]= "'" . $subcard->term . "'";
        }
        $slugs= implode(',', $slugs);
        $sub_cards= DB::get_results("SELECT id, slug, title FROM " . DB::table( 'posts' ) . " WHERE slug IN($slugs)");
        return $sub_cards;
	}