(** The ``code tail'' of an instruction list [c] is the list of instructions
  starting at PC [pos]. *)

Inductive code_tail: Z -> code -> code -> Prop :=
  | code_tail_0: forall c,
      code_tail 0 c c
  | code_tail_S: forall pos i c1 c2,
      code_tail pos c1 c2 ->
      code_tail (pos + 1) (i :: c1) c2.(** The ``code tail'' of an instruction list [c] is the list of instructions
  starting at PC [pos]. *)

Inductive code_tail: Z -> code -> code -> Prop :=
  | code_tail_0: forall c,
      code_tail 0 c c
  | code_tail_S: forall pos i c1 c2,
      code_tail pos c1 c2 ->
      code_tail (pos + 1) (i :: c1) c2.(** The ``code tail'' of an instruction list [c] is the list of instructions
  starting at PC [pos]. *)

Inductive code_tail: Z -> code -> code -> Prop :=
  | code_tail_0: forall c,
      code_tail 0 c c
  | code_tail_S: forall pos i c1 c2,
      code_tail pos c1 c2 ->
      code_tail (pos + 1) (i :: c1) c2.

Lemma code_tail_pos: forall pos c1 c2, code_tail pos c1 c2 -> pos >= 0.