Contributed by
Tom Louis Lindstrøm
I would first of all like to say that this is not primarily a novel about mathematics, but a serious exploration of central human themes such as love, loss, and loneliness. As the three main characters are all mathematicians, there is, however, a number of references to mathematics and mathematicians throughout the text, and mathematical ideas do not only inform the outlook and thought process of the protagonist, but also the structure of the novel itself.
We follow the heroine, Rakel, from her first days at university till some years after she has finished her PhD in mathematics. Along the way she befriends, and later gets involved in an affair with, a much older professor, Jakob. Quite naturally, Rakel's thoughts as well as her conversations with Jakob circle around mathematics, and among other things the reader gets an introduction to infinite cardinals; an example of a connected but not pathconnected space; a brief mention of Alexander polynomials; a proof that the sum of a rational and an irrational number is irrational; a recommendation on how to present the proof of the Snake Lemma (kick off your shoes first); and an example of how to use partition problems to attract the attention of the opposite sex. Rakel also has an interest in logical and mathematical puzzles that underscores her playful and creative approach to mathematics.
The list above may seem daunting, but the author has a light touch, and I think (although it is hard for a mathematician to say for certain) that she manages to create a picture of mathematics that is at the same time attractive, accurate, and comprehensible to nonmathematical readers. As Rakel is as interested in classical music and poetry as she is in mathematics, the text conveys an image of mathematics as an art — as something that is to be treated with the same amount of experimentation, playfulness, and seriousness as the other arts.
Most of the mathematical examples appear in the first half of the book, but in the second half, Sofya Kovalevskaya emerges as the novel's third main character. As a partly bedridden Rakel tries to fight back illness, loss, and loneliness, Sofya's story becomes a means to come to grips with her own situation and her own experiences. In Sofya's relationship to Weierstrass Rakel seeks a parallel to her own relationship to Jakob, and only towards the end of the novel does she realize that she has perhaps been trying to read too much of her own life into Sofya's. In this part of the novel, scenes from Rakel's life are interleaved with scenes from Sofya's, and the two stories reflect and contrast each other in a multitude of ways.
Since childhood Rakel has been intrigued by fractals, and with all its reflections, dilations, retractions, and inversions the novel itself takes on a fractal form. Or perhaps one might just as well call it a musical form? César Franck's sonata for violin and piano serves as a leitmotif throughout the novel, and towards the end Rakel muses:
(quoted from Lean Your Loneliness Slowly Against Mine [Lene din ensomhet langsomt mot min])
"It’s similar to what she fell for in the violin sonata by César Franck. How in the music the joy and sorrow are so tightly interwoven that it’s impossible to tell them apart. César Franck is a master of key changes. He modulates his themes, weaving them into each other and inverting them, so that they continually appear in new ways, only with a slight twist. The entire sonata has a cyclical form, where the themes from one movement appear again in later movements, but often transformed. She hopes that one day she might manage to write a novel in the same way."

For more information (including excerpts from the novel and a beautiful performance of parts of César Franck's sonata by Henning Kraggerud and Bartosz Sosnowski) I recommend the author's own video on her webpage: https://klarahveberg.no/indexeng.html. Interestingly, Literary Hub has chosen the perhaps most mathematical scene of the entire novel as their excerpt: https://lithub.com/leanyourlonelinessslowlyagainstmine/.
