Goal:
  
  A : Type
  B : Type
  P : A → Prop
  p : A → bool
  f : A → B
  g : A → B
  x : A
  l : list A
  H : P x
  H0 : Forall P l
  IHForall : forallb p l
             → (∀ x : A, P x → p x → f x = g x) → map f l = map g l
  ============================
   (p x && forallb p l
    → (∀ x : A, P x → p x → f x = g x) → f x :: map f l = g x :: map g l)


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrrewrite@0> $1 $2