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:
case not_locked_false_eq_true; Ltac.assumption
Level 1: Backtrace:

Not an inductive goal with 1 constructor.
Level 0: Backtrace:

Not an inductive goal with 1 constructor.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.