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
  l : list A
  Hl : ∀ y : C, Q y → ∥ All (P y) l ∥
  ============================
   (#|map_All fn l Hl| = #|l|)


DEBUG:Going to execute:
constr:(fun_elim)
Level 6: Backtrace:


Could not find an instance for "FunctionalElimination 
                                  (map_All fn l Hl) 
                                  ?fun_elim_ty ?n"
in
environment:
A : Type
B : Type
C : Type
Q : C → Type
P : C → A → Prop
fn : ∀ x : A, (∀ y : C, Q y → P y x) → B
l : list A
Hl : ∀ y : C, Q y → ∥ All (P y) l ∥