Simple function to list all Categories a single post is listed in

function listSinglePostCategories($post_id){

$wpcats = wp_get_post_categories($post_id);
 $cats = array();

foreach ($wpcats as $c) {
 $cats[] = get_cat_name( $c );
 }
 $lister = implode(", ", $cats);

return $lister;
}