A classic (I remember it from the mainframe I used in college):
Impure Mathematics
In George H. Scherr, ed. The Best of The Journal of Irreproducible Results, p.147. Workman Publishing, 1983
Once upon a time (1/t), pretty little Polly Nomial was strolling across a field of vectors when she came to the edge of a singularly large matrix.
Now Polly was convergent and her mother had made it an absolute condition that she must never enter such an array without her brackets on. Polly, however, who had changed her variables that morning and was feeling particularly badly behaved, ignored this condition on the grounds that it was insufficient and made her way in amongst the complex elements.
Rows and columns enveloped her on all sides. Tangents approached her surface. She became tensor and tensor. Quite suddenly, three branches of a hyperbola touched her at a single point. She oscillated violently, lost all sense of directrix and went completely divergent. As she reached a turning point she tripped over a square root which was protruding from the erf and plunged headlong down a steep gradient. When she was differentiated once more she found herself, apparently alone, in a non-euclidean space.
She was being watched, however. That smooth operator, Curly Pi, was lurking inner product. As his eyes devoured her curvilinear coordinates, a singular expression crossed his face. Was she still convergent, he wondered. He decided to integrate improperly at once.
Hearing a vulgar function behind her, Polly turned round and saw Curly Pi approaching with his power series extrapolated. She could see at once, by his degenerate conic and his dissipative terms, that he was bent on no good.
“Eureka” she gasped.
“Ho, ho,” he said. “What a symmetric little Polynomial you are. I can see you’re bubbling over with secs”.
“O Sir,” she protested, “keep away from me. I haven’t got my brackets on.”
“Calm yourself, my dear,” said our suave operator, “your fears are purely imaginary “
“i, i,” she thought, “perhaps he’s homogenous then?”.
“What order are you,” the brute demanded.
“Seventeen,” replied Polly.
Curly leered. “I suppose you’ve never been operated on yet?” he asked.
“Of course not”, Polly cried indignantly. “I’m absolutely convergent.”
“Come, come,” said Curly. “Let’s off to a decimal place I know and I’ll take you to the limit.”
“Never,” gasped Polly.
“Exchlf,” he swore, using the vilest oath he knew. His patience was gone. Coshing her over the coefficient with a log until she was powerless, Curly removed her discontinuities. He stared at her significant places and began to smooth her points of inflexion. Poor Polly. All was up. She felt his hand tending to her asymptotic limit. Her convergence would soon be gone forever.
There was no mercy, for Curly was a heavyside operator. He integrated by parts. He integrated by partial fractions. The complex beast even went all the way around and did a contour integration. What an indignity. To be multiply connected on her first integration. Curly went on operating until he was absolutely and completely orthogonal.
When Polly got home that evening, her mother noticed that she had been truncated in several places. But it was too late to differentiate now. As the months went by, Polly increased monotonically. Finally she generated a small but pathological function which left surds all over the place until she was driven to distraction.
The moral of this sad story is this: If you want to keep your expressions convergent, never allow them a single degree of freedom.
I salute you.