Goal:
  
  A : Type
  B : Type
  C : Type
  Q : C → Type
  P : C → A → Prop
  x : A
  xs : list A
  y : C
  X : Q y
  h1 : list A
  h : All (P y) h1
  ============================
   (x :: xs = h1
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in All (P y) xs)


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 := x :: xs
of type
constr
id'1 := h1
of type
constr
id' := h
of type
constr
id := h
of type
constr
cont := fun id id' => DepElim.decompose_exists id id'
        where
        id := h
        of type
        constr
of type
tacvalue of type tacvalue