In an interval notation answer, are you supposed to put a space between the two terms or not? For example, if the answer is [-1, ∞) should you write it like that or like this [-1,∞). Does it make a difference?
 A: Ideally, you should use a math typesetting system that makes these decisions for you. For instance, in the MathJax system used on this site, and more generally in the $\TeX$ system that it's based on, you'd write $[-1,\infty)$, and it comes out as $[-1,\infty)$, with a bit of a space. It would come out exactly the same if you'd write $[-1, \infty)$. Note also that this generally looks much nicer than the way you typed it, which in my view is more important than whether you put a space or not.
If you don't have the option to use such a system and you definitely need to typeset math by hand like you did in the question, I'd use a space, but I doubt that many people will notice or care.
A: I agree that it is the typesetting system responsibility to produce the right appearance. On the other hand, I think that the question is also about “what to actually write in a source code” not just about “how the rendered result should look”. People also interact with the plain text source code itself – when writing it, when reading, when reading someone's code, when communicating via e-mail or instant messenging. I think that there sould be a space after a comma in almost every case – the same way it is in normal text, the same way it is also after period, colon, semicolon, ….
