Sard went to Prof. and said, Prof. your job is very easy b'cos you are suppose to give same talk at all universities, but i have to drive hard by finding all the roots etc... Even I can present what you are presenting, so tell me what is the difficulty?
Prof. said ok and he proposed that one day I will act as driver and you act as me and deliver my talk in the university tomorrow. Sard also accepted this.
Next day at University. Prof as Sard and vice versa.
At lecture hall, Sard started giving lecture, Prof. is present there in Sard's dress. Once the lecture is over, everyone started asking doubts and questions (Sard never knew that this is the most difficult part), but he answered very nicely.
Can you guess what he would have told?
"Oh, all are very simple questions, even my driver who is sitting at last bench can answer"