Mathematical fiction is tough, because of the problems with "mathematical counterfactuals". Why not go with mathematical poetry instead? There are nice sections of same in the Clifton Fadiman anthologies. The first of these is also from The Space Child's Mother Goose. (All from memory, so please pardon any errors.)
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Three jolly sailors from Blandon-on-Tyne
Went to sea in a bottle by Klein
They found the view exceedingly dull
For the sea was entirely contained in the hull.
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There was a young lady named Bright
Who traveled much faster than light
She departed one day
In a relative way
And returned the previous night.
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There once was a fencer named Fisk
Whose movements were agile and brisk
So quick was his action
The Lorentz contraction
Diminished his sword to a disk.
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(There's also a bawdy version of that somewhere, referring to a different "sword".)
My favorite:
"Very well. Let's have a love poem, lyrical, pastoral, and expressed in the language of pure mathematics. Tensor algebra mainly, with a little topology and higher calculus, if need be. But with feeling, you understand, and in the cybernetic spirit."
"Love and tensor algebra? Have you taken leave of your senses?" Trurl began, but stopped, for his electronic bard was already declaiming:
Come, let us hasten to a higher plane,
Where dyads tread the fairy fields of Venn,
Their indices bedecked from one to n,
Commingled in an endless Markov chain!
Come, every frustrum longs to be a cone,
And every vector dreams of matrices.
Hark to the gentle gradient of the breeze:
It whispers of a more ergodic zone.
In Riemann, Hilbert or in Banach space
Let superscripts and subscripts go their ways.
Our asymptotes no longer out of phase,
We shall encounter, counting, face to face.
I'll grant thee random access to my heart,
Thou'lt tell me all the constants of thy love;
And so we two shall all love's lemmas prove,
And in our bound partition never part.
For what did Cauchy know, or Christoffel,
Or Fourier, or any Boole or Euler,
Wielding their compasses, their pens and rulers,
Of thy supernal sinusoidal spell?
Cancel me not - for what then shall remain?
Abscissas some mantissas, modules, modes,
A root or two, a torus and a node
The inverse of my verse, a null domain.
Ellipse of bliss, converge, O lips divine!
The product of our scalars is defined!
Cyberiad draws nigh, and the skew mind
Cuts capers like a happy haversine.
I see the eigenvalue in thine eye,
I hear the tender tensor in thy sigh.
Bernoulli would have been content to die,
Had he but known such a^2 cos 2 phi!
I'd completely forgotten that one!!
I just recall the (non-mathematical) poem about the haircut.
Certainly that section generally comes more to mind these days in the age of LLMs ..