About 6 months ago, when I was searching for postdoc positions, one of the professors whom I contacted encouraged me to write a joint paper to make a possibility of my invitation to his group. I tried to prepare a manuscript during this time, but as a joint work, he has not contributed yet. For instance, he has told me that he send some useful references or put some materials into the work, but never did that. I think he is no longer interested in that. What Should I do? The last time which I sent an email, he replied that he will write something about that to me "tomorrow". Today is almost 10 days after that "tomorrow".