Reminded by this last one of the professor in similar circumstances who, knowing he would be unavoidable detained for more then the 5 minutes students were expected to wait, placed his hat in advance on the lecturer's table. Nevertheless, after 5 minutes the students dispersed. The professor reprimanded them severely at the beginning of the next lecture, pointing out that his hat on the table was a symbol of his presence and they should accordingly have waited patiently for his arrival. He arrived at the lecture after that to find a lecture room empty ~ except for several rows of hats placed carefully on every desk.