Fixpoint nocc (n : nat) (l : list nat) {struct l} : nat :=
  match l with
  | Nil => 0
  | Cons m x => si nat (egal_nat n m) (S (nocc n x)) (nocc n x)
  end.

Lemma nocc_eq2 : forall (n m : nat) (x : list nat), nocc n (Cons nat m x) = si nat (egal_nat n m) (S (nocc n x)) (nocc n x).