How to categorize lots of small piece of concepts?

Hello, please forgive my poor english writing because english it’s not my first language.

I encounter some methodology issues when organizing my obsidian notes for math study.
When I learn a new math concept it usually comes with a few concepts together, extending the current concept into another direction.

For example, when I learn the math concept “Continuity”, I also encounter concepts like “Continuous on an Interval”, “Combination of Continuity”, “Continuity for common functions”, “Continuity for composed functions”, “Continuity for Inverse Function”, etc…
These concepts are somewhat similar: they all related to “Continuity” and some of them are short texts(some of them are only one-sentence long).

Currently I have two choices to organize them:

  1. Make “Continuity” a top level header(and the file name), make all other concepts sub header in the same file. But this may quickly clump up my file and its not easy to reference to, since obsidian cannot link a header directly(file name, the top level header have to be typed first then headers).
  2. Extract all sub level header into new files and make them all top-level headers. Then, make a file to link all files(a table-of-contents file). But the headache now moves to structuring file architectures. I cannot put all files(probably over 500+) into one folder, and some of the concepts are too short(one sentence or few words), that I feel like it’s just not worth to give them a single file.

Which method should I use? Or if there’s a more elegant way to do it?

I don’t really get your concerns… why wouldn’t you put 500+ notes in one folder? The beauty of Obsidian is that you can use a flat organization with no hierarchy, so why not? Also, in my opinion there is no such thing as too short for a note. You could even say if you want to honor the Zettelkasten concept you HAVE to follow the idea of atomic notes (one thought = one note). However, you certainly don’t have to… I don’t at least. :grinning: When it comes to note creation I use a mix of atomic notes, longer notes, transclusion and maps/tables of content.
You could just start crafting a note and if you write about a concept which is worth its own note, just create a new one and link it to the initial note:

Topic A:

Very interesting knowledge about Topic A but [[Topic B]] is also very interesting.

No hierarchy needed. However, if you want to impose some sort of entry notes just go with tables of content / maps of content / structure notes… however you wanna call it.