Here are a few of the more mathematical aspects of the story:

• She was a painter, and at one point speaks jealously about the pigments available to Vermeer. Her husband replies "The soul of distraction...That's painting. That's math."
• Interestingly, the story is written in "second person", with "you" referring to the deceased doctor. For example:

  (quoted from Memory Becomes You) In that lecture hall, this man who became your husband turned to you, whispered a story about his own experience with art, his visualization of numbers as points along an infinite line. What followed was the strangest few months, the both of you soaring on that ridiculous equation of two.

• Another reference to mathematics in a description of their romance when it was young:

  (quoted from Memory Becomes You) You were just out of med school, taking in the desert sun, with a mathematician, who was running imaginary numbers through eyes of needles.

• At another point, her husband says:

  (quoted from Memory Becomes You) "...You know, my love, common sense tells us there is no past, no future. Or perhaps yes, there is, but only as points along a graph. Nonexistent, except in the realm of numbers."

• When he is surprised that she beat him at chess, she says:

  (quoted from Memory Becomes You) "Next time pay attention to the board, darling. Not on endless binomials."

• Describing his research as he scribbles in a notebook at his writing desk:

  (quoted from Memory Becomes You) He furiously dances his pencil along the page, tip to tempo, over numbers revealing ... creation, in a way. Sex, you think, smiling. Shapes, supernal circles, polygons within other polygons, atomic structures, points along an elliptical.

  and

  (quoted from Memory Becomes You) There's melody to his scratchings. If you were engaged in frivolous amusement, you'd name one side of the opened page Dark Matter. The other, Sonata of the Fibonacci Golden Key. Wishing you could tell him. Wishing he could hear. Only he can't. He turns the page. At the bottom, his graphite lines shimmer in an almost phosphorescent glow; the lines, attempted answers to what light does through atmosphere, addition, subtraction, expansion, contraction. Calculus really. Equations, with their tabled certainty. Others, spilling into margins too small to contain them (Judge Fermat's phrasing of the solution to his theorem).

• There is another joking reference to Fermat's comment "I have a proof of this theorem, but there is not enough space in this margin to write it" later, but as it is about the cancer cells that are killing her being too large for her body, it is too serious a subject to be funny.

I'm not sure it's mathematical, but a major point also is a promise that she made to him when she was alive that she would return after her death to tell him about what "dark matter" actually is. Many other aspects of the story -- including the painting which gives the story its title -- connect through that idea.

Of course, there's a lot more to this short work of literary fiction than what I've said above. Like a lot of modern fiction, I suspect it is aiming to convey some truth about the human condition which cannot be directly stated in words. To see how well it achieves that goal, you'll have to read it for yourself.

This story appeared in the 2020 anthology of short fiction Shattered Fossils by the Canadian author Sharon Lax