English students... look away now.
A constant and ex are walking down a road together. Bear with me. Yes, I know, just bear with me.
Suddenly they see a differential operator. The constant gets scared and runs and hides behind a bush. Still with me?
ex says "Hey, what are you scared of?"
The constant says "It's a differential operator! He'll make me disappear!"
ex says "Look, don't worry, I'll make him go away." If you're still following this, have a cookie.
So ex goes up to the differential operator and says "Hello, I'm ex."
The differential operator says...
(Wait for it...)
(No, really, wait for it...)
"Hello, I'm d/dy."
Cheers to
lonescorpion who I swiped it from.