Goal:
    A : Type  d : A  i : nat  v : A  H : nth i [] d = v
  ============================
   ((nth_error [] i = Some v) + (nth_error [] i = None ∧ v = d))%type


DEBUG:Going to execute:
apply : eq_sym ; trivial
Level 0: Backtrace:

Proof is not complete.
Level 0: Backtrace:

Proof is not complete.