Goal:
    A : Type  i : nat  l : list A  d : A  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::ssrmove@1> $1 $2
DEBUG LTAC Evaluated term: nth_default_eq