Function VALUE

If $tau$ denotes a function with a value for the objects denoted by $tau_1$,..., $tau_k$, then the term {tt (value $tau$ $tau_1$ ... $tau_k$)} denotes the value of applying that function to the objects denoted by $tau_1$,...,$tau_k$. Otherwise, the value is undefined.
Axioms:
(Undefined (Arity Value))

(= (Value ?F @Args)
   (If (And #'?F
            (Member ?List ?F)
            (= (Butlast ?List) (Listof @Args)))
       (Last ?List)))