Goal:
  
  A : Type
  H : ReflectEq A
  l1 : list A
  l2 : list A
  l : list A
  ll1 : is_prefix (rev l) (rev l1)
  ll2 : is_prefix (rev l) (rev l2)
  _a_ : list A
  _b_ : list A
  _b1_ : list A
  ============================
   (is_prefix (rev l) _a_ → is_prefix (rev l) _a_)


DEBUG:Going to execute:
trivial; hnf; intros; (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 ])