Definition move_arg (n i j:nat) (e:Cobham) : Cobham :=
  Comp n e (move_forward i j 
    (map (Proj n) (seq 0 n)) (Proj n 0)).

Lemma move_arg_correct n i j e l : length l = n -> Sem (move_arg n i j e) l = Sem e (move_forward i j l (Sem (Proj n 0) l)).