Pustam | पुस्तम | পুস্তম🇳🇵I wasn't ready for it, lol.
The book: Introduction to Linear Algebra by Gilbert Strang, the sixth edition
the roamerLovely! Strang has a charmingly eccentric style that works well with students. The book is full of such gems. Sadly I can't find my copy right now. I remember a footnote on Gram-Schmidt orthogonalisation: "If this is what Gram found, what was left for Schmidt to do?" (from memory).
None of these little jokes and teasers are gratuitous, each aides the exposition in one way or another. A great book by a wonderful writer and teacher.