Goal:
  
  m : t
  a : t
  l : list t
  IHl : forall n : t, fold_left max l n = m -> n = m \/ In m l
  n : t
  H : max n a = m \/ In m l
  ============================
   ((n = m \/ a = m) \/ In m l)


DEBUG:Going to execute:
destruct H
DEBUG LTAC Evaluated term: IHl
DEBUG LTAC Evaluated term: or_assoc