The functions {tt adjoin} and {tt remove} construct lists by adding or removing objects from the lists specified as their arguments.
(Nth-Domain Remove 3 List) (Nth-Domain Remove 2 List)
(<- (Remove ?X ?List)
(Cond ((Null ?List) Nil)
((And (= ?X (First ?List)) (List ?List))
(Remove ?X (Rest ?List)))
((List ?List) (Cons ?X (Remove ?X (Rest ?List))))))