Hello PF, i am a first year physics student and i am taking a minor in math also, i have now a solid background in the 3 levels of calculus. I am searching for small textbooks about some mathematical topics, like in the range from 100 to 300 pages at max, as i am trying to fill my little spare time with something useful, but not overwhelming. I would also like the topics to not be covered in my courses as i don't want to study the same thing twice. I am planing to take: Linear algebra, Differential equations, Introduction to analysis, Differential geometry, and maybe topology. So give me advice outside of those topics, or just in the same topic but other directions. Thank you.