Goal:
  
  m : Z
  a : Z
  l : list Z
  IHl : forall n : Z, fold_left Z.max l n = m -> n = m \/ In m l
  n : Z
  z0 : Z
  H : z0 = m
  H0 : n < a /\ z0 = a \/ a <= n /\ z0 = n
  ============================
   (n = m \/ a = m)


DEBUG:Going to execute:
xlia zchecker