Goal:
  
  A : Type
  B : Type
  f : A → B
  IHn : nat
  l : ∀ l : list A,
        nth_error (map f l) (S IHn) = option_map f (nth_error l (S IHn))
  ============================
   (match map f [] with
    | _ :: _ :: l0 => nth_error l0 IHn
    | _ => None
    end = option_map f None)


DEBUG:Going to execute:
<coq-core.plugins.ltac::trivial@0> $1 $2

Goals:

DEBUG:Going to execute:
hnf

Goals:

DEBUG:Going to execute:
intros

Goals:

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 ]