concat_split('', abcdef).
concat_split(a, bcdef).
concat_split(ab, cdef).
concat_split(abc, def).
concat_split(abcd, ef).
concat_split(abcde, f).
concat_split(abcdef, '').
sub_atom_match(1, 3, 2).
sub_atom_match(3, 3, 0).