human
Solve the following python programming problem given the following code:
def filter_factory(global_conf, **local_conf) : 
    conf = global_conf.copy () 
    conf.update (local_conf) 
    register_swift_info ('crossdomain') 
    def crossdomain_filter(app) : 
        return CrossDomainMiddleware (app, conf) 
return <MASK> 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: global_conf, conf, local_conf
assistant
#Here is a proper replacement for <MASK>.
def crossdomain_filter(