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
  ============================
   (forall l : list A, ∥ All Q (a :: l) ∥ -> ∥ P a ∥ -> ∥ All Q l ∥)


DEBUG:Going to execute:
<coq-core.plugins.ltac::intro@1> $1