There is a related problem where many browser-based productivity tools follow design principles from websites that are trying to get clicks. For example, I commonly run into DB interfaces at work that will return, say, 10 (or 25, or other small number) results per page. Now, it’s good design to not let a query that returns, say, a million results, crash the browser. But, if a few hundred, or even a few thousand, results will display within milliseconds, why make me page dozens (or hundreds) of times? (I’m looking at you, GitHub commit history!)
Another example would be Microsoft Office’s long history of making design choices that optimize increasing “engagement with the tool” rather than making the tool unobtrusively facilitate the task. They got rid of Clippy, but now they’re into obnoxious pop-ups that are designed to call attention to some new gadget or feature.
The “click” economy has had pervasive effects on the software industry.
There are conventions pertaining to the style a letter is written in. You might have a as an arbitrary element in set A, while a<sub>1</sub>, a<sub>2</sub>, etc., are a sequence of elements in A, while fancy-boldface A or fancy-script A (I don’t know how to render those here) could represent the class of A-like sets. Also, a′ would be another case of a, or maybe the derivative of a, while a″ would be a third case, or maybe the second derivative. Sometimes superscripts or backscripts are used, when subscripts are not enough. Sometimes the Greek equivalent of a Latin letter denotes some relationship between them, e.g. ⍺ is some special version of a.
If the math goes way off into the weeds, the author might even whip out a Hebrew letter or two.