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


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