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


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.