Goal:
    T : Type -> Type  M : Monad T  A : Type  P : nat -> A -> Type
  ============================
   (forall Q : A -> Type,
    (forall (n : nat) (x : A), ∥ Q x ∥ -> T (∥ P n x ∥)) ->
    nat -> forall (a : A) (l : list A), ∥ All Q (a :: l) ∥ -> ∥ Q a ∥)


DEBUG:Going to execute:
let H := fresh x in
           intro
           H
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.
Level 2: Backtrace:

The first hypothesis in the goal is not an equality.