Goal:
  
  A : Type
  i : nat
  IHi : ∀ l : list A,
          i < #|l| → nth_error l i = nth_error (List.rev l) (#|l| - S i)
  a : A
  l : list A
  H : S i < S #|l|
  ============================
   (nth_error l i = nth_error (List.rev l ++ [a]) (#|l| - S i))


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