code: public boolean contains(Object o) {
          if (o != null) {
              for (Node<E> p = first(); p != null; p = succ(p)) {
                  final E item;
                  if ((item = p.item) != null && o.equals(item))
                      return true;
              }
          }
          return false;
      }
docs: Returns {@code true} if this deque contains the specified element.
  More formally, returns {@code true} if and only if this deque contains
  at least one element {@code e} such that {@code o.equals(e)}.
  
  @param o element whose presence in this deque is to be tested
  @return {@code true} if this deque contains the specified element