(setq x '(1 2 3 4 5)) (1 2 3 4 5) x (1 2 3 4 5) (rplaca x 10) 10 x (10 2 3 4 5) (rplaca (cdr x) 20) 20 x (10 20 3 4 5) (rplaca (cddr x) 30) 30 x (10 20 30 4 5)