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
  H : In m l
  ============================
   (In m l)


DEBUG:Going to execute:
let rec do_ccl :=
            try do_atom; repeat (do_intro; try do_atom); try arith_congr;
             (solve [ split; do_ccl ])
           in
           (solve [ do_atom | use_hyps; do_ccl ]) ||
             fail "Cannot solve this goal"