remove items appearing in both lists

Given 2 lists Olist and Clist. I want to remove items that appears in
both list. How best to do this?

Say,

(setq Olist (list "a" "b" "c" "d" "e"))
(setq Clist (list "ee" "a" "d" "c" "bb"))

i want the result to be like

(setq Olist (list "b" "e"))
(setq Clist (list "ee" "bb"))

order doesn't matter.

i think i can go thru each element and build OlistNew, and removing
Clist to build a ClistNew. But the checking existance and building
item by item would be difficult or very inefficient i think but am not
sure about lisp here.

should i turn them both into hash table first for easy checking
existance?

Thanks.

  Xah
=E2=88=91 http://xahlee.org/

=E2=98=84