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|
  H0 : #|l| - S i < #|l|
  ============================
   (nth_error (List.rev l) (#|l| - S i) =
    nth_error (List.rev l ++ [a]) (#|l| - S i))


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

File "./theories/MCList.v", line 865, characters 36-51:
Warning: Notation List.rev_length is deprecated since 8.20.
Use length_rev instead.
[deprecated-syntactic-definition-since-8.20,deprecated-since-8.20,deprecated-syntactic-definition,deprecated,default]