Goal:
    A : Type  H : ReflectEq A  l1 : list A  l2 : list A  l : list A
  ============================
   (is_prefix (rev l1) (rev (l ++ l1)))


DEBUG:Going to execute:
exists (rev l)
DEBUG LTAC Evaluated term: (f_equal rev)
DEBUG LTAC Evaluated term: (f_equal rev _view_subject_)