synchronized (mutex) {
        return delegate().removeLastOccurrence(o);
      }
    }

    @Override
    public void push(E e) {
      synchronized (mutex) {
        delegate().push(e);
      }
    }

    @Override
    public E pop() {
      synchronized (mutex) {
        return delegate().pop();
      }
    }

    @Override

      // afterDone() should be generally fast and only used for cleanup work... but in theory can
      // also be recursive and create StackOverflowErrors
      future.afterDone();
      // push the current set of listeners onto next
      next = future.clearListeners(next);
      future = null;
      while (next != null) {
        Listener curr = next;
        next = next.next;
        /*

            return new ActivationFrame(property, parent.map(child));
        }

        @Override
        public Activation transformActivation(Activation target) {
            stk.push(new ActivationFrame("activation", Optional.of(target)));
            try {
                return super.transformActivation(target);
            } finally {
                stk.pop();
            }
        }