A Mathematical Joke

Once, a constant and e raised to x (e^x) were going down a road, when they
spotted the derivative operator at a junction. The constant started
perspiring -- fully in tension. He said, "Oh ... the derivative
will convert me into zero".

e^x was cool, he said,"Ha! the derivative can't do anything to me, I am
e^x." So, in an overconfident manner, he went to the junction, while
constant stayed back.

e^x went there, and told the derivative, "I am e^x, you can't do
anything to me!"

The derivative replies back, "I'm not d/dx, I'm d/dy"