sselect[k1, k2] seq select the k1'th to the k2'th elements from the given sequence indices start from 1, not 0 also, final element has index -1, 2nd last element -2, and so on.
sselect[2, 4] ssplit |abcdefg> |b> . |c> . |d> sselect[-3, -1] ssplit |abcdefg> |e> . |f> . |g>