Goal:
  
  T : Type
  Listable_T : Listable T
  FinitelyListable_T : FinitelyListable T
  x : T
  n : nat
  offset := 0 : nat
  ============================
   (forallb (fun '(n, t) => n == find_index t)
      (combine (seq offset (length (list_all T))) (list_all T)) ->
    nth_error (list_all T) n = Some x -> find_index x = offset + n)


DEBUG:Going to execute:
<coq-core.plugins.ltac::clearbody@0> $1
DEBUG LTAC Evaluated term: enumerate_smallb
DEBUG LTAC Evaluated term: 0
DEBUG LTAC Evaluated term: n
DEBUG LTAC Evaluated term: (offset + n)