Function ADJOIN

The functions {tt adjoin} and {tt remove} construct lists by adding or removing objects from the lists specified as their arguments.
Arity: 3
Axioms:
(Nth-Domain Adjoin 3 List)

(Nth-Domain Adjoin 2 List)

(=> (Adjoin ?X ?List ?New-List)
    (= ?New-List (If (Item ?X ?List) ?List (Cons ?X ?List))))