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


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