Stroustrup - A Tour of C++. Getting a bit dated, but given how large the language has become over the decades, having a short synopsis can be quite valuable.

Friedman & Felleisen - The Little Schemer. The style doesn't work as well for me personally, but it's clearly very short and a popular way into the language and the way of thought.

Rudin - Principles of Mathematical Analysis (aka "baby rudin"). Not as short as the others, but worth the read.

F. A. Ficken - The Simplex Method of Linear Programming

K & R - The C programming language

Emil Artin - The Gamma Function

Emil Artin - Galois Theory. It has a super brief chapter on linear algebra and determinants that is extremely on-point.

A. I. Khinchin - Mathematical Foundations of Information Theory

makes sense - but note: especially with receipts, there are use-cases where a tax authority might come back 7+ years later, or where heirs might need the proof after your passing (!) - and if they don't have it, it might cost them very large amounts of money in taxes.

thanks for sharing - what do you use for colorization?