Goal:
    A : Type  v : A
  ============================
   (((∃ n : nat, hd_error (skipn n []) = Some v) → False)
    ∧ (False → ∃ n : nat, hd_error (skipn n []) = Some v))


DEBUG:Going to execute:
solve
[ do
![ solve
 [ trivial | apply : eq_sym ; trivial ]
 | discriminate
 | contradiction
 | Ltac.split ]
| case not_locked_false_eq_true; Ltac.assumption
| match goal with
  | H:¬ _ |- _ => solve [ case H; trivial ]
  end ]