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


DEBUG:Going to execute:
let ty := type of B in
           intro || (let H := fresh 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.