As a resident of post-Brexit Britain, I was horrified as I read this expecting it to have the opposite punchline and to turn into an anti-immigration joke.
For those that don't know, Polish (and other Eastern European) migration was a major issue raised by some in the Brexit campaign.
A more horrific and offensive version of the joke, which I actually saw recently as output from fortune [1], adds a part about the contour integral of the whole of Europe still being zero because the Poles are removable.
For those that don't know, Polish (and other Eastern European) migration was a major issue raised by some in the Brexit campaign.