Definition instr_approx_rel (n:nat) (i1 i2:instruction) : Prop :=
  fmap_instr (K.approx n) i1 = fmap_instr (K.approx n) i2.

Lemma intro_instr_approx_rel : forall m n i, m >= n -> instr_approx_rel n i (fmap_instr (K.approx m) i).