Goal:
  
  T : Type
  Listable_T : Listable T
  FinitelyListable_T : FinitelyListable T
  x : T
  n : nat
  ============================
   (find_index x = n -> nth_error (list_all T) n = Some x)


DEBUG:Going to execute:
<coq-core.plugins.ltac::intro@0>