Goal:
    A : Type  l : list A  d : A
  ============================
   (∀ (i : nat) (v : A),
      nth i l d = v
      → (nth_error l i = Some v) + (nth_error l i = None ∧ v = d))


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrelim@0> $1 $2
DEBUG LTAC Evaluated term: v
DEBUG LTAC Evaluated term: i