def set_to_delete(set_list):
    """
    Return the set to delete given a list of sets.

    It keeps the first element of the set.

    >>> set_to_delete([{1, 2, 3}, {4, 5}]) # it keeps 1 and 4
    {2, 3, 5}
    """
    return {element for group in set_list for element in list(group)[1:]}