def reflexive_closure_function(rel, universe):
    """
    Function to return the reflexive closure of a relation on a set
    :param rel: A list that is a relation on set universe
    :param universe: A list that represents a set
    :return: A list that is the  relexive closure of the relation rel on the set universe
    """
    return rel + [(x, x) for x in universe if (x, x) not in rel]