: (setq Lst (3 4 5 6))
-> (3 4 5 6)

: (push 'Lst 2)
-> 2

: (push 'Lst 1)
-> 1

: Lst
-> (1 2 3 4 5 6)

: (insert 4 Lst 'X)
-> (1 2 3 X 4 5 6)