Are you a Doctor ?

A girl was walking on the side walk. She sees a man lying on the street, needing immediate help. The victim says that he is having a heart attack. The girl asks people around the street. And a man approached.

Girl: Help, are you a doctor?

Man: I am a doctor. What’s going on?

Girl: A Heart Attack!

Man: I am doctor in mathematics.

Girl: He is going to die.

Man: Prove it!