Goal:
  
  A : Type
  B : Type
  C : Type
  Q : C → Type
  P : C → A → Prop
  fn : ∀ x : A, (∀ y : C, Q y → P y x) → B
  x : A
  xs : list A
  h : ∀ y : C, Q y → ∥ All (P y) (x :: xs) ∥
  H : ∀ (H := CoreTactics.block) (l : list A) (Hl : 
                                               ∀ y : C, 
                                                 Q y → ∥ All (P y) l ∥),
        {| pr1 := xs; pr2 := map_All_obligation_2 x xs h |} =
        {| pr1 := l; pr2 := Hl |}
        → map_All fn xs (map_All_obligation_2 x xs h) = map_All fn l Hl
          → let H0 := CoreTactics.block in #|map_All fn l Hl| = #|l|
  ============================
   (let H := CoreTactics.block in #|map_All fn (x :: xs) h| = #|x :: xs|)


DEBUG:Going to execute:
cbn beta in hyp