Simplified Common Lisp reference
Symbol class: Sequences (Lists, Strings) and Arrays
Symbol type: function
subseqseqstartend(optional) => sequence
Argument description:
seq a sequence
start bounding index
end bounding index, default NIL

SUBSEQ function makes new sequence as a subseqence of argument. Default ending index is end of sequence. See also COPY-SEQ and MAP.

SUBSEQ may be used with SETF.

(subseq "hello world" 3) => "lo world"
(subseq "hello world" 3 5) => "lo"
(let ((a "hello world")) (setf (subseq a 3 5) "LO") a) => "helLO world"
(let ((a "hello world")) (setf (subseq a 3 5) "YYY") a) => "helYY world"
Function indexFull documentation for subseq (HyperSpec)