Goal:
    A : Type  B : Type  a : A  l : list A  default : A  H : S #|l| = 0
  ============================
   (mapi
      (λ (i : nat) (_ : B),
         match i with
         | 0 => a
         | S m => nth m l default
         end) [] = a :: l)


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 ]