I think this would work both at the logical level (e.g., the concept of azimutal angle in a xyz-coordinate system) and as a stylesheet level (theta for physcisits, and phi for mathematicians).

Such annotations would really help with browsing math content—you can see what prerequisites concepts are used in a paper from its import statements, without the need to read the whole thing. Also, you could browse from the other end (reverse-imports / uses), looking for docs that make use of a given concept.