Thanks. Just to clarify, my issue is with 'set-assignment' and not setf. I doubt if there are the same functions!
ctrl-tab short cut does not give me the documentation for set-assignment. I also searched in utility bar.
Example:
(setf trans '((5/4) (-1/4 1) (-3/8 7/8) (-1/2 3/4) (-7/12 2/3)
(-2/3 7/12) (-3/4 1/2) (-13/16 7/16) (-7/8 3/8)
(-15/16 5/16) (-1 1/4)))
(setf mat (make-omn
:pitch (reverse ; reverse the pitches
(integer-to-pitch '(0 1 2 3 4 5 6 7 8 9 10 11)))
:length trans))
(setf sets (set-assignment 'mat mat))
(rnd-sample 8 (list mat0 mat3 mat5 mat8 mat10))