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:
PTRDEBUGTACsimplify * || simplify ?