def get_integer_form(elem_list):
    """For an element list like ['e1', 'a1_2', 'a1_1', 'a1_3'],
    return the integer 213, i.e., the 'subscripts' of the elements that
    follow the identity element."""
    return int(''.join(map(lambda x: x.split("_")[1], elem_list[1:])))