This is a subject I struggled with the first time I took it. Ironically, this was the engineering version of it. It wasn't until I took the rigorous, axiomatic version that everything clicked.

Let A be a function algebra on a locally compact Hausdorff space. A linear isometry T: A → A is said to be of codimension 1 if the range of T has codimension 1 in A. In this paper, we provide and ...

I've been grading calculus exams this week, and even though my students did quite well overall there were a couple of errors that I see every semester. Errors that make mathematicians' heads explode.