human
Solve the following python programming problem given the following code:
def _sort_factors(factors, **args) : 
    "Sort low-level factors in increasing 'complexity' order. " 
    def order_if_multiple_key(factor) : 
        (f, n) = factor 
        return (len (f), n, f) 
def order_no_multiple_key(f) : 
        return (len (f), f) 
if args.get ('multiple', True) : 
        return sorted (factors, key = order_if_multiple_key) 
else : 
        return sorted (factors, key = <MASK>) 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def order_no_multiple_key(