Definition max_var_nformulae (l : list (NFormula Z)) :=
  List.fold_left  (fun acc f => Pos.max acc (max_var xH (fst f))) l xH.Definition F (acc : positive) (f : Pol Z * Op1) := Pos.max acc (max_var 1 (fst f)).

Lemma max_var_nformulae_mono_aux : forall l v acc, (v <= acc -> v <= fold_left F l acc)%positive.