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
  a : A
  l : list A
  allq1 : list A
  allq : All Q allq1
  ============================
   (a :: l = allq1 ->
    let H := CoreTactics.block in let H0 := CoreTactics.block in Q a)


DEBUG:Going to execute:
try rename id into id',id' into id
Level 3: evaluation returns
try rename id into id',id' into id; cont id'1 id
where
t := a :: l
of type
constr
id'1 := allq1
of type
constr
id' := allq
of type
constr
id := allq
of type
constr
cont := fun id id' => DepElim.decompose_exists id id'
        where
        id := allq
        of type
        constr
of type
tacvalue of type tacvalue