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:
<coq-core.plugins.ltac::discriminate@0>
Level 0: Backtrace:

Cannot apply lemma eq_sym
Level 0: Backtrace:

Cannot apply lemma eq_sym
Level 0: Backtrace:

Cannot apply lemma eq_sym