Goal:
  
  T : Type -> Type
  M : Monad T
  A : Type
  P : A -> Type
  Q : A -> Type
  f : forall x : A, ∥ Q x ∥ -> T (∥ P x ∥)
  l0 : list A
  a : A
  l : list A
  ============================
   (∥ All Q (a :: l) ∥ -> ∥ P a ∥ -> ∥ All P l ∥ -> ∥ All P (a :: l) ∥)


DEBUG:Going to execute:
<coq-core.plugins.ltac::intro@0>