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


DEBUG:Going to execute:
now left
DEBUG LTAC Evaluated term: max_le'