Fixpoint fib n := match n with
| O => 1
| S m => match m with
| O => 1
| S o => fib o + fib m end end.
Ltac sleep n :=
try (assert (fib n = S (fib n)) by reflexivity).
(* Tune that depending on your PC *)
Let time := 18.

Axiom P : nat -> Prop.
Axiom P_triv : Type -> forall x, P x.