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