def transitive_closure_function(rel, universe):
    """
    Function to determine the transitive closure of a realtion
    :param rel: A list that represents a relation
    :return: The transitive closure of a relation
    """
    result = rel
    changed = True
    while changed:
        changed = False
        for a in universe:
            for b in universe:
                for c in universe:
                    if (a, b) in result and (b, c) in result and (a, c) not in result:
                        result.append((a, c))
                        changed = True
    return result