Goal:
  
  A : Type
  P : A → Type
  x : A
  l : list A
  p : P x
  h : All P l
  e : Some x = Some x
  IHh : ∀ (i : nat) (x : A), nth_error l i = Some x → P x
  ============================
   (P x)


DEBUG:Going to execute:
<coq-core.plugins.ltac::clear@0> $1