Goal:
  
  A : Type
  P : A → Prop
  Q : A → Prop
  p : A → bool
  x : A
  l : list A
  H : Q x
  HQ : Forall Q l
  Hp : ∀ x : A, Q x → reflect (P x) (p x)
  IHHQ : Forall P l → forallb p l = true
  x0 : A
  l0 : list A
  H0 : P x0
  HP : Forall P l0
  ============================
   (x :: l = x0 :: l0
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in forallb p (x :: l) = true)


DEBUG:Going to execute:
simplify * || simplify ?; cbv beta