К этому

A constant function and exp(x) are walking around.
Suddenly, Constant spots at a differential operator crawling on the wild side and whispers to exp(x) :
- “Look, a differential operator. If he meets me, I am cooked.”
And Cste starts running like hell.
On her own, exp(x) gets no fear.
She crosses the street and drawls proud as punch :
- “hey ! I’m exp(x), and you are ?..”
while the operator looks up and answers
- “hi ! I’m d/dy.”