intuition.
unfold F_randomFunc.
destruct (arrayLookup_f _ y (F x z)); wftac.
Qed.

(* Specifications: *)
Theorem randomFunc_mem_wf :
forall (A B : Set) x y z (w : list (A * B)) v,
well_formed_comp z ->
well_formed_comp (randomFunc_mem x y z w v).
Theorem randomFunc_mem_wf :
forall (A B : Set) x y z (w : list (A * B)) v,
well_formed_comp z ->
well_formed_comp (randomFunc_mem x y z w v).