Goal:
  
  A : Type
  x : A
  xs : list A
  f : A → bool
  H0 : ∀ f0 : A → bool,
         (λ (x : A) (_ : In x xs), f x) = (λ (x : A) (_ : In x xs), f0 x)
         → forallb_InP xs (λ (x : A) (_ : In x xs), f x) = forallb f0 xs
  ============================
   (locked false = true)


DEBUG:Going to execute:
fun => <coq-core.plugins.ltac::assumption@0>