Goal:
    A : Type  H : ∀ x : A, In x [] → bool  f : A → bool  l : list A
  ============================
   (∀ g : ∀ x : A, In x l → bool,
      g = (λ (x : A) (_ : In x l), f x)
      → {| pr1 := []; pr2 := H |} = {| pr1 := l; pr2 := g |}
        → true = forallb_InP l g
          → let H := CoreTactics.block in forallb_InP l g = forallb f l)


DEBUG:Going to execute:
simplify * || simplify ?