I'm kind of desperate as well.. been working on this for the past one week but can't work out the answer.. Construct a procedure that take two list p, q and return a list that contain reverse order of p and q. But it should not create new cons cells. e.g. (revert (list 1 2 3) (list 4 5 6)) produce (3 2 1 4 5 6) Would be grateful if anyone could point out some pointers or solution.