Ltac id_compare x y :=
  destruct (CompSpec2Type (Ident.compare_spec x y)).Ltac id_comp x y H1 H2 H3 :=
  destruct (CompSpec2Type (Ident.compare_spec x y)) as [H1|H2|H3].

Lemma id2pos_inj x y : id2pos x = id2pos y -> x=y.