def get_union_over_keys(map_to_set):
    """Compute the union of the map range values.
    
       For a map whose range is a set, union the range
       over keys in the map return the resulting set.
    """
    result = set()
    for key in map_to_set:
        value_set = map_to_set[key]
        result |= value_set;
    return result